We generated > 10(7) mast cells by culturing 10(7) cord blood mononuclear cells for > 10 weeks in the presence of Steel factor, interleukin-6 and prostaglandin E2. 99% of the cultured cells had tryptase-positive granules, while 18% had chymase-positive granules. Cultured mast cells contained 3.6 micrograms histamine and 3.5 micrograms tryptase per 10(6) cells. Cells sensitized with 1 microgram/ml human IgE released 58.5% histamine and 1.55 ng tumor necrosis factor (TNF)-alpha per 10(6) cells when challenged with 1 microgram/ml antihuman IgE, whereas the control cells spontaneously released 3.7% histamine and 0.18 ng TNF-alpha. Analysis for surface antigens revealed that cultured mast cells expressed the following CD molecules: 9, 13, 14, 29, 33, 38, 43, 44, 45RA, 45RB, 46, 47, 48, 49d, 50, 51, 53, 54, 55, 58, 59, 60, 61 and 117 (c-Kit). Taken together, these cultured cells seem to be functionally mature mast cells.