Adult rats were given water with sodium fluoride (10 mg/l) during 7 weeks before pregnancy, during pregnancy and after the delivery. The born rats were treated in the same manner and were investigated 1, 2, 4 and 6 months after birth. It was found that exposure to sodium fluoride stimulated an increase of hydroxyproline and hydroxylysine concentration in serum and the urinary excretion of these catabolites. A decrease of soluble and insoluble collagen was shown in skin and lungs of exposed animals as compared with controls. The decrease of collagen in tissues was not age-dependent.