In the present paper physico-chemical and analytical studies on penbutolol sulfate (Hoe 893d) are reported. In addition to an interpretation of ultraviolet and fluorometric spectra, data are given regarding the dissociation constant, solubility, distribution, and protein binding. The substance and its major metabolte, as well as their glucuronides, are detectable by means of a selective fluormetric method. Moreover, mention is made of the results of a human pharmacokinetic study.