Chronic actinomycetoma associated with grain production was induced in BALB/c mice by subcutaneous inoculation of live Nocardia brasiliensis in Freund incomplete adjuvant into the hind footpads. Similar inoculation of N. asteroides and N. caviae resulted in local tumor formation which healed spontaneously after 5 months, the disease disseminating into the peritoneum, where masses or organisms could be detected. Grains were recovered from superficial skin lesions of N. caviae, but not from the N. asteroides-infected mice. Mycetoma lesions, appearing as early as 1 month after inoculation of 1.2 X 10(7) colony-forming units of N. brasiliensis per ml or as late as 3 months with inoculation of 1.0 X 10(5) colony-forming units per ml, became persistent and were readily detectable even 6 months after inoculation. No spontaneous healing occurred, and grains were recovered at different stages of the disease. Saline suspensions of N. brasiliensis also produced typical mycetoma lesions, although the incubation period was ca. 6 months. Adjuvant addition appeared to accelerate the onset of the disease. Experimental production of actinomycetoma in laboratory animals allows the study of many unanswered aspects of the disease and also provides a suitable model for therapeutic trials in the search for new and more effective chemotherapeutic agents.