The effects of storage in an automatic counting and dispensing machine on dissolution rates on five drug products with known or suspected bioequivalence problems were studied. Amitriptyline hydrochloride, digoxin, prednisone, hydrochlorothiazide, and tolbutamide tablets exposed and unexposed to automatic counting machines were collected from 10 pharmacies located in various parts of the country. A 60-tablet unexposed sample was taken from a previously unopened container and placed in a tight, light-resistant container. Another 60-tablet sample of the same brand and lot number was collected 30 days after the initial filling of the counting machine or when it had to be refilled, whichever came first. Each sample was tested for dissolution rate and content uniformity. Twenty-seven paired samples representing 23 lots from 10 manufacturers were collected. There were no substantial differences in dissolution rate or content uniformity between the exposed and unexposed samples. Average temperatures in the pharmacies during the three-month sampling period ranged from 72 to 79 degrees F. Storage times of the drug product samples in the automatic counting machines varied from 9 to 46 days. The environmental conditions to which these tablets were exposed had no noticeable effect on the dissolution of these formulations.