Illnesses associated with seafood are an important public health concern worldwide, particularly considering the steady increase in seafood consumption. However, research about the risks associated with seafood products is scarce in developing countries. Histamine fish poisoning is the most common form of fish intoxication caused by seafood and usually presents as an allergic reaction. This condition occurs when fish are not kept appropriately refrigerated and histamine is formed in the tissues. Histamine levels of >500 ppm usually are associated with clinical illness. We assessed histamine levels in fish from markets in Lima, Peru, with a quantitative competitive enzyme-linked immunosorbent assay. Thirty-eight specimens were purchased from wholesale and retail markets: 17 bonito (Sarda sarda), 16 mackerel (Scomber japonicus peruanus), and 5 mahi-mahi (Coryphaena hippurus). Seven fish (18%) had histamine levels of 1 to 10 ppm (three mackerel and four bonito) and three (8%) had >10 ppm (three mackerel, 35 to 86 ppm). Fish from retail markets had detectable histamine levels (>1 ppm) more frequently than did fish bought at wholesale fish markets: 9 (36%) of 25 fish versus 1 (8%) of 13 fish, respectively (P=0.063). Higher histamine levels were correlated with later time of purchase during the day (Spearman's rho=0.37, P=0.024). Mackerel purchased at retail markets after 2 p.m. had a 75% prevalence of histamine levels of >10 ppm. Mackerel purchased late in the day in retail markets frequently contained high histamine levels, although the overall prevalence of elevated histamine levels was low. Despite the small sample, our findings highlight the need to reinforce seafood safety regulations and quality control in developing countries such as Peru.