The immunotoxicological effects of cadmium suggest that it may alter immunosurveillance. However, the studies contributing to this conclusion have been conducted at relatively high cadmium concentrations and for extended periods of exposure. Cadmium was administered in the drinking water of Balb/c mice at 0.01, 0.10, and 1.0 ppm for 4 to 5 wk. Under these conditions, there was a cadmium dose-dependent change in the mortality rate of mice when challenged with an intraperitoneal injection of 5 X 10(3), 5 X 10(4), or 5 X 10(5) MOPC-104E plasmacytoma cells. There was a maximum decrease in mortality at the 0.01 ppm dose level, while at the higher cadmium concentrations there was little or no change. At the two highest tumor cell doses, there was a decrease in the incubation time of the illness in animals exposed to 0.01 ppm cadmium. This returned to control values at the higher concentration of cadmium. The data indicate that at very low concentrations cadmium can alter tumor growth by more than one mechanism that may involve immunocompetence.