Physical factors which might influence spawning site selection and hatching success in anadromous rainbow smelt (Osmerus mordax) were investigated. Water depth, water velocity, distance upstream, stream temperature, tide height, and estimated spawning time accounted for 33% of the variation in egg deposition in one stream and 14% in a second stream. Multiple linear regression of egg deposition on physical factors showed water velocity, distance upstream, temperature, and estimated available spawning time had regression coefficients significantly different from zero. Hatching success in laboratory experiments ranged from 15 to 34% in 1972 and 17 to 61% in 1973. Analysis of variance in percentage hatch indicated eggs incubated on sand had significantly lower hatching success than eggs incubated on two sizes of gravel or on an artificial spawning substrate. Differences in effective circulation within incubation jars apparently caused variations in time to hatching.