(1) The effects of the neurotoxin 3-acetylpyridine on the levels of soluble proteins and enzyme activities in various tissues of Japanese quail were investigated. (2) SDS-polyacrylamide gel electrophoresis showed that in the brain the soluble proteins with a molecular mass corresponding to 18 kDa were increased in quail treated with this toxin. The soluble liver proteins with the largest molecular masses (200, 120, 98, 80.5 and 58 kDa) were either missing or present at lower concentrations in the treated group compared to those in the controls while those of lower molecular mass (62, 55, 45, 36.5 and 24 kDa) were found to be present in higher concentrations. Similarly, treatment with 3-acetylpyridine tended to decrease the concentration of soluble proteins in pectoral muscle having a high molecular mass (160, 98, 60, 33, 30.5, 22 and 14 kDa) and to increase those having a low molecular mass (26, 20, 19.5 and 16 kDa). (3) There was a marked reduction in the treatment group in the concentration of NAD in pectoral muscle but not in other tissues. A similar observation was also made with total RNAs levels. (4) The specific activity of malic enzyme and glyceraldehyde-3-phosphate dehydrogenase was markedly reduced in the liver and pectoral muscle of the treatment group but was not affected in other tissues. The specific activity of 6-phosphogluconate dehydrogenase was significantly lower in the liver only, and that of lactic dehydrogenase and acetylcholinesterase was not affected in any of the tissues examined. (5) The results suggest that the metabolic actions of 3-acetylpyridine are quite distinct from those shown by niacin deficiency and its analog such as 6-aminonicotinamide.