AbstractAggregations of Con A binding sites that occur on the surface of preconjugant cells have been studied in order to reveal their possible functions in the conjugation process. By means of a newly adapted horseradish peroxidase method, they can be visualized in distinctly shaped oval fields (OF) as soon as 10–15 min after mixing cells of opposite mating types. Cycloheximide (CHX) prevents establishment of new OFs but does not effect preexisting ones. In the absence of previously developed OFs, cells cannot form pairs. However, even if OFs are fully present, pairing still can be inhibited by CHX, high K+ concentrations (≥ 60 mmol/liter), or the K+‐channel blocker tetraethyl‐ammonium (TEA, 10 mmol/liter). A doublet cell with OFs on both halves normally binds to one singlet. This partner, after a stay of 10 min in an angled agglutination position, quickly rotates into the parallel pairing position. At this moment, the doublet suddenly loses its affinity for complementary cells at its free OF. This behavior explains why many doublets pair only with one singlet. The Con A binding sites themselves seem not to be active in cell pairing; they are regarded as a marker for a region of the cell surface whose contact with a complementary cell subsequently results in the unmasking of unidentified compounds that serve as adhesive agents and/or the hinge for the quick rotation of agglutinated cells.