A study of population exposed to hexachlorobenzene (118741) (HCB) was conducted. The cohort consisted of 204 members of the Turkish population, 132 males, who were inadvertently exposed to HCB treated wheat between 1956 and 1958. At that time, seed wheat coated with fungicides containing 10 percent HCB was distributed in southeastern Turkey. Some of the fungicide coated wheat was used for bread or bulgar, resulting in a severe outbreak of porphyria. The subjects were clinically examined; urine, feces, and blood assessments of porphyrins and HCB, and routine laboratory tests were conducted. Dermatologic symptoms ranked in decreasing order of prevalence induced severe scarring, hyperpigmentation, hirsutism, pinched faces, and fragile skin. Short stature, small hands, and painless arthritis were also observed. Porphyric and neurological symptoms included general weakness, paresthesia, myotonia, and enlarged liver. Thirty three of 132 males and 43 of 72 females had enlarged thyroids. Twenty three subjects gave a vague history of excreting red or brown urine in the previous 2 years; however, urinary porphyrins were elevated in only three subjects. Only 20 of 140 samples of human milk contained less than 0.02 part per million (ppm) HCB, the maximum allowable limit established by the World Health Organization. Preliminary results of a subchronic and chronic study of HCB in weanling Sprague-Dawley-rats were also presented. The rats were fed 0 to 150ppm HCB for up to 2 years. Renal cell adenomas and carcinomas, liver hepatomas, hemangiomas, hepatocarcinomas, and bile duct adenomas and carcinomas were found. A generalized leukemia was also observed. The authors recommend further studies to assess the impacts of HCB and other chlorinated hydrocarbons on human health and the environment.