The effects of Corynebacterium cutis extract on lymphocyte transformation, phagocytic activity and antibody level were studied in 4-months-old buffalo calves vaccinated against Brucella abortus using strain 19 vaccine. The results revealed that treatment with C. cutis extract, either 3 days prior to or concurrently with the vaccine evoked a significant elevation of lymphocyte stimulation indices in the presence of phytohaemaglutinine, concanavaline-A and Brucella abortus soluble antigen as well as significant increase in the phagocytic activity of mononuclear cells against Candida albicans. Antibody levels were estimated by rivanol and serum tube agglutination test. Administration of C. cutis extract before or simultaneously with the vaccine provoked a marked elevation of antibody titre. Conversely, C. cutis injection one week postvaccination, did not elicit any important alterations in either cell mediated or humoral immune responses.