Miniature Sinclair swine bearing cutaneous melanomas and nonmelanoma bearing littermate controls were tested for lymphocyte blastogenic response in a microculture assay. Lymphocytes were assayed for 3H-thymidine incorporation following stimulation with concanavalin A, phytohemagglutinin or pokeweed mitogen. Treatment with all mitogens revealed a significantly (p less than 0.05) reduced proliferative capacity in melanoma swine as compared to littermate controls. These results lend further support for the use of miniature Sinclair swine as a research model for human melanoma.