The Kurnakov test, also known as Kurnakovs reaction, is a chemical test that distinguishes pairs of cis- and trans-isomers of [PtAX] (A = NH, X = halogen or pseudohalide). Upon treatment with thiourea, the trans-dihalides give less soluble white products, whereas the cis'-dihalides give more soluble yellow products. The test is still used to assay samples of the drug cisplatin, but it is mainly of pedagogical interest, as it illustrates the trans effect.
The test was devised by Soviet chemist Nikolai Kurnakov.