With the health aspect in civ 4 biological warfare has got to be added as a downside (or upside) to the 'Genetics' tech. Spys poisoning populations with virilant strains of anthraxs sums up the future of war pretty accurately. This is how I think it should work: 1. I think an attack should randomly set at an increase of between +10 to +20 on target city for a random turn number between 3-20. 2. this is determined by Total ammount of target city + total excess of civilisation. So the higher the science in the city and the more health concious the civilisation as a whole the lower the and the shorter the outbreak. 3. Whether the outbreak spreads to another city is determined by firstly how far away the city is from the original host city. Then by the cities total nect by your whole civ's total excess . 4.plus a quaratine bonus determined by combined of military units garrisoned in that city. The more points that racked up by these determining factors the less likely the diesease will spread to that city. So you see a scientific, health concious civ with a large garrisoned military will probably survive a biological okay. (Incidentally, in real life biological attack we'll all throw up our own intesines all over our children while trying desperately to shield their swollen pustulant faces from the "burning".) However, if you neglect health and are not as up to speed on science and the fighting men are all away in some war leaving a small garrison in your hinterland cities you might be in big trouble. A powerful and long term outbreak might escalate into a multicity pandemic that guts your civilisation slowly and painfully. However, I would make it only really effective due to gross mismanagement on part of the enemy civ and with grave diplomatic penalties from other 'softy' AI civs if used. It wouldn't be that expensive to execute as biotech weapons are scarily cheap in comparison with, say, nukes. With +20 for 20 turns you can imagine the affect on the city... Here are some more details on my proposed model for bio warfare: 1.Another nuance of my 'outbreak' model will be that desease knows no culturally boundaries. That rivals cities can also be affected just as much as your own cities. 2.This would inturn have an effect on diplomancy with an 50% biological defense bonus for cities with closed borders with an infected civ. 3.Another aspect would be the military units actually in the target city at time of infection. These infantry and calvary units should lose 10% of thier strength each subsequent infected turn. 4.To make this less devastating, all vehicles waste down to a derelict 0 strength, and remain immovable until the infection lifts, and then it repairs as normal. If derelcit vehicles are attacked by enemy forces they are appropiated like workers into their own forces, however, the capturing enemy unit would become infected also. 5. An obvious tactic could be used by sending your infected units out to infect enemy cities in a crazed kamakazee dash into their territory. However once they leave their cities the units will die, including the vehicles, even after the infection had been brought under control. 6. The 'genetics' tech should therefore have a bio-warfare rapid response gun powder unit that has only a 10% chance of becoming infected. The unit should have 2 movement pts and be about as strong as mobile infantry. 7. Another possibility would be a 'black death' aspect that would function in much the same way as 'bio warfare' except the desease would occur randomly only in cities with more than, say, +8 excess . Hence, the medieval era would be peppered with small outbreaks and maybe one, pan continental plagues if every one is filthy. Unit tactics could be used but without counter-bio warfare units. Just think of the amusing cat and mouse game that would ensue if an infected city emptied its sickly units across your borders in a bid to take you with them. 8. Expansionist trait would be greatly improved, also trade in giving resources. 9. I must stress that I don't particularly think bio warfare or desease should be too effective or prevalent as it would be really annoying to pull loads of troops back to form quarantine zones. In the most part, I envisage its use as another form of slightly unstable collateral damage, sofening up the city before the ground force moves in. Furthermore, desease was a medieval weapon of war, insofar as carcusses of animals were catapulted into besieged castles and even groups of venerial deseased prostitutes were cunningly offered to the enemy only to later infect their fighting men. 10. It also gives a greater reason to research future tech in the late game inorder to immunise your civ further.