The influence of temperature on the kinetics of immunoglobulin-positive (Ig+) leukocytes in cell suspensions prepared from the pronephros and the intestine of common carp Cyprinus carpio during the development of Goussia carpelli, a gut-dwelling coccidian parasite, was examined. The development of the parasite was temperature dependent. At 20 C, oocysts were formed 2-3 wk postexposure (PB), at 15 C for 3-4 wk PE, and at 12 C for 5-6 wk PE. At all 3 temperatures, changes of relative numbers of Ig+ cells were observed in cell suspensions. During merogony and gamogony, the proportion of Ig+ cells increased, peaked during oocyst formation of the parasite, and then remained elevated. Serum collected from infected carp 8-20 days PE contained immunoglobulins binding to G. carpelli merozoites. The development of the parasite and the increase of Ig+ cells in intestine and pronephros of infected carp were temperature dependent. The peak level of Ig+ cells appeared not to be influenced by temperature. These findings indicate that even at low temperatures local and systemic immune responses are induced in carp with enteritic parasite infection.