Two new stocks of the hypotrichous ciliate Euplotes octocarinatus isolated in Florida and Maryland/USA were identified as members of mating type VI (mt 2mt 3), secreting pheromones 2 and 3 and mating type VII (mt 1mt 1), secreting pheromone 1. These are two out of the ten already known mating types of Euplotes octocarinatus. Results of breeding experiments suggest that the new stocks belong to new syngens of this species complex. The analysis of the macronuclear molecules containing the new pheromone 1, 2 and 3-encoding genes show that their structure is very similar to those isolated before. Like in these genes the coding regions are interrupted by three introns with a high degree of homology. A comparison of the deduced amino acid sequences of the new pheromones with the known versions of the corresponding pheromones reveals homologies of 76 to 93% for the secreted proteins whereas the leader sequences are 98 to 100% identical. In both versions of pheromones 1, 2 and 3 there are ten cysteine residues which are located at strictly conserved positions. In spite of their differences both versions of pheromones 1, 2 and 3 show the same specific biological activity. This might be an indication that the unchanged residues participate in receptor binding.