The market-share rule has been applied by courts when there is known negligence that results in injury to the plaintiff, but the negligence cannot be attributed to any one of several defendants, each of which is equally likely to have caused the injury but none is separately more likely than not to have caused the injury. The rule has been applied when several pharmaceutical firms manufactured an identical drug, marketed under different names, that is linked to plaintiff's injury, but it isn't known which of the names of the drug actually caused the injury. Under the market-share liability rule, the defendants, if negligent, would be liable for that share of the plaintiff's award that corresponded to their respective share of the market. Several problems result from the application of the market share rule. For example, because the individual defendant is either responsible for a certain share of plaintiff's injury or not, the application of the rule can result in mistaken findings linking probable responsibility with complete or partial liability. In addition the market-share rule confuses the likelihood that defendant's breach caused plaintiff's injury with the likelihood that there is a causal link between the breach and the injury. Suggestions are made for improving the application of the market-share rule. 18 footnotes.