Following the outbreak of organomercury poisoning in Iraq, an investigation was carried out during the spring and summer of 1972 to evaluate environmental contamination by organomercury.Analyses were performed on fish of several species (not typical predators) and on a few specimens of aquatic birds (not fish-eating). Most fish samples contained concentrations in muscle ranging from 0.01 to 0.15 mg/kg. These concentrations are within the range found in tropical rivers. Higher figures, 0.3-0.5 mg/kg, were found downstream from a caustic soda plant south of Baghdad. A few cases of very high mercury concentrations (25-30 mg/kg) were reported from an area where fish kills had occurred. Aquatic birds (ducks and waders) contained low concentrations of mercury (900-2750 ng/g). Tail feathers of seed-eating birds were found to contain 13 500-21 000 ng/g of mercury, which is about 10 times higher than values reported from Ethiopia and within the range found in Sweden and Canada. Insect-eating birds contained 1850-5200 ng/g, which is thought to be slightly elevated. Extremely high concentrations of mercury were found in muscle tissue of dead seed-eating birds (15 000-40 000 ng/g), while feathers contained similar concentrations (9000-52 000 ng/g). These extremely high concentrations were found only in the vicinity of storehouses where treated seed was kept. No birds of prey could be caught and analysed.