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Concentrations of mercury, lead, zinc, iron, chromium, cadmium and copper were determined in sediment profiles from Jequiá mangrove, a polluted region of Guanabara Bay in Brazil. Methylmercury concentrations were also determined, together with the ratios of methylmercury to total mercury (% MeHg). The mangrove is influenced by a polluted creek and estuarine waters. In general, 87% of the concentration of lead, iron, chromium, cadmium and copper was determined not to be bioavailable due to the elevated organic carbon and sulphide content in sediments. For most of the contaminants studied, the sediment enrichment factor for metals was high (cadmium, 650; lead, 450; copper, 250; chromium, 170; zinc, 24; mercury, 9). Sediment samples did not contain high concentrations of methylmercury (range 3.11–9.74 ng MeHg g⁻¹ dry wt) or total mercury (0.52–2.38 mg THg kg⁻¹ dry wt). Total mercury (THg …