The stability of aspirin in propoxyphene compound capsules made by three manufacturers, stored under a variety of temperature and humidity conditions, was compared. The cotton packing was removed from 100-capsule bottles, and the containers were stored (capped) under the following conditions: 25 c37 C and 50 C at both high (90%) and low (10%) humidity. No desiccant was removed from the bottles if originally present. The products tested were Darvon Compound-65 (two formulations) (Lilly), SK-65 Compound (Smith Kline & French) and Dolene Compound-65 (Lederle). Under all conditions, the stability of aspirin in the SK-65 Compound product was greater than that of Darvon Compound-65 which in turn was greater than Dolene Compound-65. Further, the rate of aspirin decomposition was greater in the latter product than in the others.