In all biological systems, the information content of hormonal signals is conveyed by the modalities of pulsatile hormone secretion. New mathematical tools for the analysis of pulsatile behaviour and increasing knowledge of the sources of signal variability have enabled us to recognize altered hormonal pulsatility associated with human disease. Its consequences for our understanding of disease mechanisms, for diagnostic procedures and for therapeutic decisions are discussed at the level of single hormones. Increased disorderliness of hormone secretion is a hallmark of pituitary adenomas, indicating functional subsystem autonomy. The effects on target tissues of changing growth hormone therapy from low-frequency administration to long-acting preparations are still incompletely understood. In contrast, the gonadotropic axis is a paradigm for the successful therapeutic use of induced pulsatility changes, where therapy with long-acting gonadotropin-releasing hormone (GnRH) agonists suppresses endogenous gonadotropin pulses and gonadal function, and pulsatile GnRH administration is used to restore normal gonadal function. Future development of endocrine therapies will depend on our knowledge of hormonal pulsatility.