Relaxin (RLX) belongs to the relaxin hormone super-family, which in humans includes 3 RLX molecules and 4 insulin-like peptides. Of these, luteal RLX is the main circulating form in animals and man. RLX, formerly known for its effects on reproduction and pregnancy, has been demonstrated to act on numerous other targets, including the cardiovascular, central and peripheral nervous, respiratory, tegument, excretory and digestive systems. Most of these effects have been studied in animal models, but there is compelling evidence that RLX also acts in the human. Over time, RLX, as a crude or purified extract from corpora lutea or as a pure molecule produced by chemical synthesis or recombinant DNA technology, has been the object of clinical studies aimed at identifying its possible therapeutic fields of application. The availability of human recombinant RLX and the most recent achievements on its biological effects, especially on connective tissue remodelling and cardiovascular physiopathology, have sparkled a novel peak of interest of clinicians to the therapeutic potential of RLX. This review of the existing clinical studies with RLX is focused at its pharmacological and toxicological features, with the aim to support interest of clinicians and pharmaceutical companies to continue the pathway which may eventually succeed in translating RLX from the laboratory bench to the bedside.