Chroococcidiopsis occurred as a phycobiont in members of the lichen family Lichinaceae. The phycobionts isolated from Anema nummularium (strain 26322a PH), Peccania sp. (strain 26370a PH) and Psorotichia sp. (strain 26391c PH) proved to be three different strains of Chroococcidiopsis, a genus of blue-green algae (cyanobacteria). The mode of division and reproduction was studied in cultures of the algae. The non-motile baeocytes ('endospores'), which are characteristic of the genus, were produced by multiple fission either of secondary or tertiary mother cells. Within particular strains the mode of development varies. In strain 26322a PH, baeocytes were formed only by secondary mother cells; in strain 26370a PH, both types occurred. In strain 26391c PH, baeocytes were produced by two forms of secondary mother cells: globose mother cells with an irregular arrangement of baeocytes and by clusters of four mother cells with more or less regular arrangement of baeocytes. It is not possible to identify capsoid blue-green algae phycobionts of lichens without culture studies.