To determine changes in the contents of some heavy metals (Cd, Zn, Cu) in the fish Ariopsis bonillai, at Ciénaga Grande de Santa Marta, Colombia, monthly samples were taken between July 1987 and June 1988. The highest concentrations in the muscle appear between November and February (4.24 micrograms Cd/g, 109.4 micrograms Zn/g and 13.3 micrograms Cu/g), during the periods of lower salinity, at the end of the rainy season, and at the beginning of the dry season. Metals were measured also in the liver: values for Zn and Cu were ten times higher than in the muscle. About the first half of the year, the values tend to be similar. Cd differences were not as strong as for the other metals.