Chemical Laboratory, Bihar National College, Patna Manuscript received 29 June 1973 ; revised 30 July 1973 ; accepted 7 January 1974 Fourteen thioindigoid dyes have been prepared by the condenstion of 4-iodothioindoxyl and 7-iodothio­indoxyl (in two cases) with various ortho diketones. 4:4'-Diiodothioindigo has also been prepared. The spectral and other properties of the dyes have been studied and compared with those of the isomeric 5-iodo, 6-iodo and 7-iodo substituted dyes.