The workers' compensation systems of several states have been expanded in recent years to include injuries and diseases caused by cumulative injury and occupational stress. This expansion has placed a financial burden on the respective systems, on employers, and on consumers, who ultimately must pay the cost of claims through higher priced products or services. This expansion may not be justified from a social perspective, however; extant medical and sociological evidence is not conclusive as to whether occupational-stress injuries or diseases--such as coronary heart disease, hypertension, stroke, and neuropsychiatric illness--are the direct result of stressful work environments. Using the California workers' compensation system as a model, the authors submit that the underlying premises of liability governing the expanded systems should be reassessed based (1) on economic factors, specifically, the increasing costs of workers' compensation; (2) on the capacity of the system to process an ever-increasing number of claims; and (3) on the principle on which workers' compensation systems were established, that of equity between the employer and the employee. On the basis of these three factors, the authors evaluated three legislative approaches to restructuring the expanded system: presumption of compensability, apportionment of liability, and threshold of compensability. The first recognizes that although certain health problems are related to the workplace, the degree of causation is difficult to prove; under this approach, therefore, causation is presumed, and injury compensated, for all diseases and injuries that the system defines as work related. The second holds that where a causal relationship between the work and the injury can be proved, the employer nevertheless should be responsible only for that portion of the disability actually caused by the workplace. The third directs that the injured employee be compensated only when a direct causal link between the job and the injury or disease can be proved. The authors recommend that legislators implement this third alternative. For one reason, it is feasible economically; for a second, it would not burden the system or increase litigation; for a third, it is equitable to both employees and employers.