In describing physiochemical properties of interfacial interactions, the interfacial tension is a major parameter. In the case of biological or body fluids, the presence of surface active substances influence the value of the surface tension. Thus, several proposals have been made for methods to investigate the changes in surface tension. Alterations of surface tension (compared to those of the normal values, e.g. of amniotic fluid) may indicate a pathophysiological status. This report presents data of systematically measured surface tensions of a few physiological fluids. Problems of methodology and data interpretation are discussed together with suggestions for new approaches, and comparisons are made with previously reported measurements.