AbstractTo investigate the role of cilia in mating interactions ofTetrahymena thermophila, ciliary membrane‐rich fractions were isolated from two wild‐type strains, a non‐discharge mucocyst mutant which possesses mating behavior similar to wild‐type, and a mating mutant which is able to costimulate cells of complementary mating type but cannot enter into pair formation. In each case, proteins from the ciliary membrane‐rich fractions of starved, mating‐competent (“initiated”) cells were compared with those from non‐starved, mating‐incompetent (“non‐initiated”) cells, by gel electro‐phoresis and lectin blotting. In stained gels, a 43 kDa polypeptide was reduced or absent in initiated cells but present in non‐initiated cells, in all strains. In silver‐stained gels, a 25 kDa polypeptide was present in all strains, both initiated and non‐initiated. In blots probed with Con A‐peroxidase, a 25 kDa glycoprotein was present in ciliary membrane fractions from non‐initiated cells and absent in membranes of initiated cells of the two wild‐type strains and the mucocyst mutant, but is present in initiated and non‐initiated cells of the mating mutant (several hypotheses are presented to explain these findings). In addition, ciliary proteins of the mating mutant included at least two unique Con A‐binding polypeptides. Our results support the idea that development of mating competence during starvation involves an extensive remodeling of ciliary membranes, and identify a 25 kDa glyco‐conjugate as having a potential role in control of pair fo