Studies of the effects of cholera toxin on the intestine have produced conflicting results regarding stimulation of IgA secretion. In the present study rabbit ileal loops were perfused with saline, and the IgA content of the perfusate was assessed by immunoradiometric assay. Crypt epithelial IgA content in biopsies was studied by immunofluorescence. Cumulative loop fluid IgA production 300 minutes after exposure to cholera toxin was 6216 +/- 993 microgram/cm compared with 4646 +/- 953 microgram/cm in controls (P < 0 . 20). However, rate of fluid IgA production above baseline at 300 minutes was 1742 +/- 181 microgram/h/cm in cholera loops and 1049 +/- 310 microgram/h/cm in controls, and the mean difference between the cholera and control loops was statistically significant (P < 0 . 05). In biopsies, mean rank of crypt epithelial IgA at 300 minutes was decreased compared with controls (P < 0 . 05). The findings of increased rate of fluid IgA production and decreased epithelial IgA suggest that a single dose of cholera toxin enhanced secretion of IgA from crypt epithelium into the intestinal lumen, although the magnitude of the enhancement was not great.