The isomeric composition of iridodial in three species of dolichoderine ants has been determined. All contained more than 80 per cent of a single isomer. Two species, Iridomyrmex pruinosus analis (E. Andre) and Tapinoma sessile (Say), also produce iridolactones of the configuration of the major iridodial isomer. Two varieties of Conomyrma pyramica contain 6-methyl-5-hepten-2-one. © 1968.