Departamento de Ciencias Químicas y Fisiológicas, Sede Santiago Sur, Universidad de Chile, Casilla 3931, Santiago, Chile CONTENTS PAGE Introduction 287 Pre-transcriptional aspects of the mechanism of action of androgens 288 Binding of androgens to plasma proteins 288 The metabolism of androgens in the androgen-sensitive tissues 290 The binding of androgens to cytoplasmic receptors 291 Prostate 292 Kidney 293 Muscle 293 Bone marrow 294 Skin 294 Urogenital tract of the embryo 294 The binding of androgens to other cytoplasmic components 295 The nuclear binding of androgens 296 Nuclear receptor sites 296 Nuclear acceptor sites 298 Transcriptional and post-transcriptional aspects of the mechanism of action of androgens 299 Action on chromatin template capacity and activity 299 Action on RNA polymerase 301 Action on biosynthesis and pool size of RNA precursors 302 Action on RNA maturation 302 Action of androgens on protein biosynthesis 303 Action of androgens on DNA synthesis 304 Some comments on the effect of androgens on transcriptional and post-transcriptional events 304 General remarks 305 References