The latency associated with the transforming growth factor-betas (TGF-betas) was discovered in 1984. Since the two publications on this subject in that year, there has been on average over sixty reports in which latency was the dominant theme for each of the past 10 years, proof enough of the interest in this field of growth factor research. As the mature 25 kD forms of the TGF-betas are required for them to exert their many, diverse biological effects, it was inevitable that an explanation of the structure and of the activation of the latent complexes be sought. This overview provides a description of these essential points. Now that it has been clearly shown that dysregulation of particular components of the TGF-beta signalling pathway is implicated in many human diseases, the activation of the latent TGF-beta complexes has taken on added importance. Technical improvements enable the distinction of active and latent TGF-beta proteins in vivo and have started to reveal anomalies in the control of activation in relation to various pathological situations.