Chick embryos were cultured in hemispheric dishes containing 25 ml fresh albumen. The addition of albumen, known to the relatively poor in free calcium, increased the deficit of calcium regularly observed in embryos cultured with other methods. In spite of this, the embryos survived and differentiated adequately for prolonged periods of time. Most of the cultured embryos presented malformations of the long bones of the limbs consisting of bowing and exuberant growth of bone trabeculae in the concavity of the bend. Block staining with alizarin showed that bones were undermineralized at the time in which bending occurred. Leg muscles differentiated adequately as judged from their electron microscopical observation. It is concluded that the malformations result from the action of normal muscles on undermineralized bones. The growth of bone trabeculae at the concavity of the bend probably results from the piezoelectrical stimulus produced by the bending of the bones. The concentrations of both the ionized and bound fractions of blood calcium were significantly reduced in the cultures. The system appears to constitute an adequate model for further explorations on the effects of prolonged hypocalcemia on the differentiation of different tissues and organs.