Notropis volucellus volucellus and N. stramineus stramineus are morphologically similar, especially in areas of sympatry. I investigated the morphological, biogeographic and reproductive relationships between them in Manitoba and Southern Ontario. I wished to determine which characteristics could be used reliably to distinguish between them in zones of allopatry and sympatry and to determine what, if any, reproductive isolating mechanisms function in zones of sympatry. Weekly collections were made at several sites in Ontario in 1987 and 1988, and in Manitoba in 1989 and 1991. Standard characteristics of field caught and museum specimens were subjected to discriminant function analysis to determine which characteristics discriminated between the species as a whole, between species within province, within species between province, and between allopatric and sympatric populations of both species in Ontario. The species were more distinct from each other in Manitoba than in Ontario. Ontario and Manitoba populations of N.s. stramineus were more distinct than Ontario and Manitoba populations of N.s. volucellus. Both allopatric and sympatric populations of the two species were more similar to heterospecifics from the same type of site than they were to conspecifics from the other type of site. Sympatric populations were largely allochronic, both in site use and sexual maturation, or were numerically dominated by one or the other species. Gonadosomatic indices of both sexes were plotted against water temperature and compared between populations over time. In both provinces in both species testes matured at 15C and threshold temperature for spawning was 18-20C. Allopatric populations of both species in Ontario and N.s. stramineus in Manitoba were sexually mature by the start of the collecting season. Allopatric populations of both species in Ontario have prolonged spawning periods, and N.s. stramineus may be a multiple spawner. Manitoba populations of both species have single, relatively short spawning periods.