In the pre-vitellogenic oocytes of the hibernating lizard Lacerta sicula, a fraction of the ribosomal population crystallizes in the form of ribosomal bodies (RB). In these oocytes the rate of protein synthesis is 35–75 % lower than in the oocytes of the summer animals in which the RB have dissolved. The isolated RB are able to respond to Poly(U) and are also active in the endogenous protein synthesis in a cell-free system. This contrasts with the in vivo situation, where they appear to be completely inactive in protein synthesis. The possibility that RB represent a regulatory mechanism of protein synthesis is discussed.