PKC comprises a superfamily of isoenzymes that is activated in response to various stimuli. Hyperglycaemia induces the activation of different PKC isoforms. However, the PKC-B isoform appears to be preferentially activated by high glucose levels and has been shown to be associated with diabetic vascular complications. In vitro and in vivo animal studies have shown that ruboxistaurin mesylate, a novel selective inhibitor of PKC-B ameliorates the biochemical and functional consequences of PKC activation and may have the potential to reduce the burden of vascular complications associated with diabetes. Results of the first phase-II and phase-III trials evaluating the efficacy of this compound on diabetic microvascular complications have been published recently. They confirm that this compound may favorably influence the evolution of diabetic microvascular complications.