Hormones produced by haploid cells of one mating type of T. mesenterica and inducing conjugation tubes in the other mating type have been studied in preparation for isolation and identification. The active material can be extracted from aqueous solution with n-butanol, but not with less polar solvents, and is adsorbed on cation and anion exchange resins, charcoal, and neutral polystyrene resin. The molecular weight is probably less than 1000. Three active components can be separated by silica gel column chromatography with a gradient of water in ethanol, or by paper chromatography. The conjugation hormones may be non-polar amino acids or small peptides.