Abstract2,3‐Substituted 5‐methyl‐4‐thiazolidinones (1) and 3‐substituted 5‐methyl‐2,4‐thiazolidine‐diones (II) were prepared by reacting some carbodiimides with α‐mercaptopropionic acid, with the purpose of obtaining potentially chemotherapeutic agents. It is noteworthy that 3‐cyclohexyl‐5‐methyl‐2,4‐thiazolidinedione (IId) was obtained in three different crystalline structures. Some secondary compounds were also obtained: theN,N‐disubstituted ureas (III) and thioureas (IV) in all cases, the dianilides (V) and the tri‐substituted guanidines (VI) from the arylcarbodiimides, and the dithiolactide (VII) from the isop