Absorption and passage through the dense layer of plasma membranes of rat hepatocytes and rabbit red blood cell ghosts, steroid hormones labelled with 3H were studied. The degree of absorption of steroid hormones by plasma membranes decreased in the following succession: progesterone greater than testosterone greater than oestrone greater than prednisolone greater than oestriol. The degree of the hormone absorption correlated with the solubility in lipids and with the effect of the enzyme release from the lysosomes. At the same time it is in inverse ratio to the speed of passage through the dense layer of the membranes. The nature of absorption of the steroid hormones is independent of the origin of plasma membranes.