Chain modification of a thiazolidinone prostaglandin isostere has led to the production of 4-[3-[3-[2-(1-hydroxycyclohexyl)ethyl]-4-oxo-2-thiazolidinyl]propyl] benzoic acid (5b) which at 1 mg/kg po in the conscious dog causes a 70% increase in renal blood flow over control values with a duration of action exceeding 5 h. Preliminary testing indicates that 5b has a relatively specific action on the vasculature of the kidney. The enantiomers of 5b have been separated and the renal vasodilatory activity has been found to be entirely a property of the R-(+) enantiomer.