More than 160 taxa representing 41 genera were identified from this extensive first time inventory of rotifers from inland lakes of northern lower Michigan. About 30 species of planktonic rotifers (36 species of total rotifers) were found per lake based on 8 collections (1 per season) for a 2 year period (summer 1973-winter 1975). This unusually large number of species may reflect the advantage of the year around sampling routine. Eight of the 75 planktonic species (11%) were endemic to North America. Large oligo-mesotrophic lakes contained nearly twice the number of planktonic species (34) as small, hypereutrophic bog lakes (18). Wildlife impoundments had the greatest number of planktonic species (39) and greatest number of total species recorded (65). Summer and fall collections contained approx. 60% of the total numbers of species found per lake whereas winter and spring collections had only 32% and 47% of total species, respectively. The inventory produced 2 new species in the genera Notholca and Keratella suggesting a high probability that many undescribed species still exist in Michigan and in the United States. Detailed taxonomic surveys of the zooplankton of the United States have not been undertaken so that biogeography and species diversity are poorly known. The rotifer communities of each lake can be reconstructed from figures and tables making this inventory an important benchmark for evaluating future regional environmental change.