The present review describes the biological activities of synthetic thiirane-containing (TC) carboxylic (fatty) acids. More than 30 biologically active TC fatty acids are lipid metabolism regulators, radioprotectors, or hypolipidemic agents, and they also show other pharmacological activities. The structures and predicted activities of a selection of TC fatty (carboxylic) acids are reported. Also, some additional activities are predicted with the computer program PASS, based on structure–activity relationships (SAR), which point toward new possible applications of these lipids. This article emphasizes the role of the TC carboxylic (fatty) acids, as an important source of leads for drug discovery.