Summer production estimates were made for the rotiferPolyarthra vulgarisin a northern Michigan bog lake. Egg development times for the rotifer at 15 and 21-C were 1.3 and 1.17 days respectively. The dry weight of an individual rotifer was 0.24 ug. Production ranged from 0.0 ug/L/day to 26.9 ug/L/day throughout the summer of 1977. Average production estimates forP. vulgarisduring the period were 2.34 ug/L/day using Edmondson's egg ratio method of calculation, and 4.61 ug/L/day using Galkovskaya's generation time method.