Toxoplasma gondii is an obligate intracellular parasite that infects a wide variety of nucleated cells in its numerous intermediate hosts including man. The oral route is the natural portal of entry of T. gondii. Ingested organisms are released from cysts or oocysts within the gastrointestinal tract and initially invade the intestinal epithelium. We show that T. gondii invades and proliferates in cultured primary rat enterocytes, obtained with an original procedure. Activation of the enterocytes with rat recombinant interferon-gamma (IFN-gamma) inhibits T. gondii replication, the inhibition being dose dependent. Neither nitrogen and oxygen derivatives nor tryptophan starvation appear to be involved in the inhibition of parasite replication by IFN-gamma. Experiments using Fe2+ salt, carrier and chelator indicate that intracellular T. gondii replication is iron dependent, suggesting that IFN-gamma-treated enterocytes inhibit T. gondii replication by limiting the availability of intracellular iron to the parasite. Our data show that enterocytes probably play a major role on mucosal surfaces as a first line of defence against this coccidia, and possibly other pathogens, through an immune mechanism. The results suggest that limiting the availability of iron could represent a broad antimicrobial mechanism through which the activated enterocytes exert control over intracellular pathogens.