The leucocyte migration test from caillary tubes was examined for its usefulness as an assay for cell-mediated immunity in melanoma patients. Formalin fixed melanoma cells either obtained from established cell lines or freshly excised tumors were used as antigen source. From a group of 33 melanoma patients 14 reacted positively (42%) when fixed cultured cells were used, whereas, no positive reactions were found in a group of 14 control donors. However, a considerable proportion of patients with chronic inflammatory processes of the skin reacted positively (4/17 = 24%). A smaller proportion of positive reactions were found in melanoma patients when fixed melanoma cells from excised tumors were used (1/16 = 6%). The positive results in the group with chronic inflammatory processes may be explained as reactions against melanoma associated, but not melanoma-specific, antigens. Three possible reasons are discussed for the low frequency of positive reactions with cells from excised tumors: 1. the cells used in this study display only a few of the antigenic determinants typical for malignant melanoma, 2. antigen expression is quantitatively lower. 3. the surface antigens are covered by blocking factors.