Abstract This study was undertaken to investigate the cellular effects of Cd and metallothionein (MT) metabolism using a primary cell culture system composed of isolated rainbow trout ( Salmo gairdneri) hepatocytes. The cells were exposed to 89 n m Cd for 0, 5, 12, 20, 25, 30, 35, and 40 hr at 15°C. The concentration of Cd used did not cause significant cell damage, as estimated by lactate dehydrogenase (LDH) release into the extracellular medium. However, the presence of the metal led to increased cellular levels of calcium within the first 12 hr of incubation. Later, these returned to control values and remained as such for the rest of the examination period. A transient increase in intracellular copper and zinc also occurred during the initial incubation period. In parallel, the hepatocytes were found to accumulate appreciable quantities of Cd, a significant proportion of which were detected in the cytosol. Distribution profiles of cytosolic Cd obtained through Sephadex G-75 chromatography showed that the metal was associated mainly with the high-molecular-weight (HMW) and middle-molecular-weight (MMW) protein fractions. At t = 12 hr, there was a maximum in the proportion of Cd in the MMW fractions, which was accompanied by a decrease in the proportion of Cu in the same fractions. At this time, cellular MT exhibited the highest levels. MMW fractions were further resolved using anion-exchange chromatography. Although Cd was present in the peaks corresponding to MT, the data indicated that these peaks also contained detectable amounts of Cu and Zn. The results describe a series of changes pertaining to metal and MT metabolism in hepatocytes exposed to “subcytotoxic” levels of Cd.