A recently developed method for demonstration of antigen‐dependant migration inhibition, the agarose plate technique, and skin tests were used to demonstrate delayed hypersensitivity towardsMycobacterium tuberculosis and Nocardia farcinicain guinea‐pigs. Peritoneal exudate cells from animals immunized withM. tuberculosis and N. farcinicadisplayed immunologically specific inhibition of migration after stimulation with tuberculin andN. farcinicasensitin, respectively. The slight cross reactivity between the two antigens demonstrated by skin tests was also observed with the agarose technique. Previous skin testing did not influence migration inhibition of peritoneal exudate cells. Migration inhibitory activity of supernatants of tuberculin stimulated lymph node cells from guinea‐pigs which had been immunized withM. tuberculosiswas demonstrated on peritoneal exudate cells from non‐immunized