1. The morphological changes of the pancreas induced by administration of dl-ethionine were determined for treated rats and for a group of pair-fed untreated controls in order to separate the direct effect of dl-ethionine from the effect of accompanying reduction of food intake. 2. Adult male Wistar rats were studied in 3 groups of 10 animals each: 1) fed ad libitum and treated daily with dl-ethionine (35 mg/100 g body weight, ip) for 10 days; 2) treated daily with vehicle (saline) as group 1 and pair-fed to group 1; 3) treated daily with vehicle (saline) and fed ad libitum. Two rats from each group were killed on days 2, 4, 6, 8 and 10 to characterize the pancreas in terms of morphological properties using morphometric analysis. 3. Exposure to dl-ethionine induced a progressive and significant decrease in both pancreas weight and acinar cell number and volume. Pair feeding induced less pronounced decreases in pancreas weight and acinar cell volume. Pancreas weight was 125 mg/100 g body weight for dl-ethionine-treated vs 205 mg/100 g body weight for pair-fed controls and 320 mg/100 g body weight for ad libitum-fed controls after 10 days. Acinar cell number (x +/- sigma/square root of n): 175 x 10(6) +/- 28.4 per micron3 for dl-ethionine-treated vs 221 x 10(6) +/- 17.3 per micron3 for pair-fed controls and 271 x 10(6) +/- 23.9 per micron3 for ad libitum-fed controls.(ABSTRACT TRUNCATED AT 250 WORDS)