Useful thiazolidines include the drug pioglitazone, the antibiotic penicillin, and N-Methyl-2-thiazolidinethione, an accelerator for the vulcanization of chloroprene rubbers.

[4] Thiazolidines functionalized with carbonyls at the 2 and 4 positions, the thiazolidinediones, are drugs used in the treatment of diabetes mellitus type 2.

Rhodanine is a related bioactive species, featuring one carbonyl and one thiocarbonyl.

With cysteine, a buffered water solution of the aldehyde changes from yellow to colorless due to a secondary ring closing reaction of the imine.

Homocysteine is unable to give ring closure and the color does not change.