This volume contains the text of the main lectures given by interna tionally recognized scientists at the Tenth European Workshop on Mo lecular and Cellular Endocrinology of the Testis, held in Capri, Italy, from 28 March to 1 April 1998. Topics include spermatogonial transplantation, germ stem cell biol ogy, regulation of meiosis and spermiogenesis, growth factors, cell sig naling and transduction, steroidogenesis, androgen-regulated genes, sperm activation and sperm factors active at fertilization and the mo lecular basis of specific pathologies of the testis. Looking back at the previous 'Capri edition' (1986), the lectures of which were published by Elsevier, it is perhaps not surprising to notice that many of the top ics addressed at that time are basically the same now. On the other hand, it appears evident that the search for experimental models of sig nificant physiological value to study testicular function has advanced greatly. In this connection, the use of genetically manipulated animal models in the study of the regulation of spermatogenesis and of the en docrine role of the testis represents a core part of the present volume. The authors deserve our special thanks not only for delivering ex cellent state-of-the-art lectures, but also for providing their manuscripts well before the meeting.