A floristic survey from December, 1968, to September, 1971, provided a record of the communities of attached algae in Lake Mize, Florida. Counts and estimates of organism densities were used to determine the relative abundance of species. In all, 89 species were identified and monitored during the study period. Both quantitatively and qualitatively, desmids and filamentous Chlorophytes were usually an important part of the periphyton in Lake Mize. Several acidiophilic diatoms were abundant at certain times, while Cyanophytes generally reached high frequencies only during the July to September period. In the course of the investigation, it was determined that algal species employing particular modes of attachment were more abundant under some conditions than others. Generally, tightly adhering, resupinate forms attained higher densities on glass slides than filamentous and loosely associated metaplanktonic species. Conversely, the epiphytic flora of the filamentous sedge, Websteria suhmersa, contained a large number of both strong and weak attachers. Other broad-leafed macrophytes in the lake normally had an epiphytic flora composed mainly of filamentous and/or resupinate species with somewhat fewer metaplanktonic algae than the flora of W. submersa. However, no absolute substrate specificity could be shown for any one species or by any attaching form. A major observation to come from this investigation was that the attached flora varied not only with substrate type, but that different areas of the lake supported somewhat different periphyton communities. In calmer areas of the lake or in protected enclosures, metaplanktonic and filamentous species were more abundant on all substrates than in areas subjected to currents and turbulence. When clean substrates (slides or plants) were submerged, the pioneering attachers were usually the most abundant resupinate and/or filamentous forms in the lake at that time. Debris became associated with the attached algae community for a period up to 5 weeks. The number of metaplanktonic species increased as well as total algal frequencies. In excess of 3 to 5 weeks, peeling ensued with a subsequent loss of debris and algae, especially debrisassociated metaplanktonic forms. Whereas the type of substrate and the amount of current appeared to be critical in determining whether weak attachers would be present in a given periphyton community, light was also important in governing the floristic composition of the community in Lake Mize. Chlorophytes were generally abundant only in the upper 6 to 18 inches of the lake. Chrysophytes, on the other hand, had a broader vertical range, frequently remaining common to a depth of 30 inches on glass and 42 inches on W. submersa. In the case of Cyanophytes, light requirements were variable. Some species were restricted to the upper 6 to 18 inches of the lake and others were common to a depth of 42 inches. A comparison of the attached flora in Lake Mize, Florida, a dystrophic lake, with that of the mesotrophic Elk Lake, Minnesota, revealed a number of differences. Taxonomically, the attached floras of the two lakes were almost completely different with only three species common to both lakes. Diatoms formed the major part of the attached flora in Elk Lake, while Chlorophytes were generally the dominant algal division in Lake Mize. In Lake Mize, light was a severely limiting factor with attached algae usually restricted to the upper 30 to 42 inches of the lake and with maximum algal frequencies occurring in the upper 6 to 18 inches. In Elk Lake, attached algae were common to a depth of 4 meters. Maximum frequencies usually occurred at a depth of 3 meters.