Pregnant mice were injected with pharmacological doses of vitamin A during days 11-19 of gestation with the purpose of studying the long bones of offspring up to the age of 1 week. Tibiae were collected for routine light microscopic examination and tranmission electron microscopic examination. In addition, biochemical studies were conducted to determine the calcium, phosphorus, and magnesium content as well as the hydroxyproline and protein content of the bones. Treatment with vitamin A resulted in reduced weight and length of the long bones, as well as the presence of excessive calcification throughout the hypertrophic zone of the cartilaginous epiphyses. Matrix vesicles, many of them containing hydroxyapatite crystals, were observed and found to be distributed within the cartilaginous epiphyses in a similar pattern as in untreated control mice offspring, but mineral crystals were also observed unassociated with the matrix vesicles. The calcium, phosphate, magnesium, and hydroxyproline content was reduced in the vitamin A offspring. However, the percentage of these minerals expressed per dry weight bone was higher than in controls, verifying the morphological findings that although vitamin A inhibits bone growth, it enhances calcification in the growth plate.