The Kolyuk cave lies in the southern part of Hungary in the Mecsek Mountains, about 3 km. in distance from the village of Mànfa. The material accepted for investigation originated from a recently discovered and until now completely entombed part of the cave. It was collected by the geologist Gàbor Magyari and consisted of material scraped from the walls and ceiling of a cavity in the cave, which could be reached only by underwater swimming. From these scrapings cultures were installed with sterile Knopp solution and after the algae present in the collection reproduced, a diversified flora developed which consisted of the following: Cyanophyta - 20 species, varietates and formae; Bacillariophyta - 2 species and varietas; Chlorophyta - 7 species. There was a total of 29 different taxa. Since the cave from which the collections were made was completely devoid of light, it is especially significant that a well developed blue-green algal flora was found. We thus have further evidence for our previously advanced theory (Claus, 1955, 1962 a, 1962b) that some algae were present in the caves at the time of their origin. They were able to survive in an actively assimilating vegetative state and not only in the form of cysts or arthrospores.