Topical application of citral on male rat skin induces hyperplasia of the sebaceous glands. Ultrastructural study showed that this hyperplasia is manifested by an increase in number of the partially differentiated cells of the gland. Citral was found in fat droplets of the mature differentiated and partially differentiated cells. Because citral causes an increase in testosterone level, we conclude that the sebaceous gland hyperplasia is related to androgen activity.