Five different dog mastocytoma tumors were successfully transplanted and propagated in BALB/c nude mice. Cells from two of these tumors were passaged serially through at least four generations of mice without morphological or functional change. The average yield from a 2-cm tumor harvested from a mouse was 1.2 +/- 2.8 X 10(9) mast cells with greater than 90% viability. Cells of one line were larger and more heavily granulated than the other, and contained 1.29 +/- 0.74 pg histamine/cell (mean +/- SD). Calcium ionophore A23187 and compound 48/80 caused dose dependent histamine release with no significant difference in release from generation to generation. The smaller cells contained 0.06 +/- 0.06 pg histamine/cell. Histamine release after calcium ionophore or compound 48/80 was dose dependent and unchanged through serial passages. Following passive sensitization antigen caused dose-dependent histamine release confirming the presence of IgE receptors on these cells. In both cell lines histamine release was inhibited by terbutaline, dibutyryl adenosine 3',5'-cyclic monophosphate, or isobutylmethylxanthine. These methods provide a morphologically and functionally stable population of nearly pure canine mast cells for biochemical and physiological studies.