In order to determine endocrinologic changes by obesity in patients with polycystic ovarian disease (PCOD) and to assess the involvement of peripheral ~-endorphin in the pathogeneis of PCOD, levels of plasma ~-enorphin, gonadotropin. androgen and prolactin were measured by radioimmunoassay. Thirty-one PCOD patients (21 normal weight. 10 overweight) and 27 normally ovulating women. 20 normal weight. 7 overweight (normal controls) were studied. There were no significant differences in the plasma gonadotropin, androgen, and prolactin levels between the overweight and normal weight group in PCOD patients and normal controls. No significant difference in plasma fJ-endorphin levels was found between normal weight controls and normal weight patients. Plasma ~-endorphin levels were similar in overweight controls and patients. These values were significantly higher than those in normal weight controls and patients respectively. There was a significant correlation between plasma ~-endorphin levels and the percentage of ideal body weight in patients with PCOD and normal controls. These data suggest that peripheral opioid abnormality in PCOD may be a phenomenon associated with obesity and not related to the pathogenesis of disease.