The relationship between a geometric series of ten initial densities (Pi) of Rotylenchulus reniformis, (mixtures of eggs, juveniles and immature females) from 0 to 64/cm3 soil, and growth of cowpea (Vigna unguiculata) cv. Blackeye was investigated in two-litre clay pots. Fitting the Seinhorst model, y=m+(1-m)zPi-T, to average weight of seeds produced gave a tolerance limit (T) to the nematode of 0.12 eggs, juveniles and immature females/cm3 soil. Minimum relative yields (m) for weight of seeds produced was 0.65 at Pi=16 nematodes/cm3. The maximum rate of nematode reproduction was 32.2-fold and occurred at the lowest initial population density. The highest final population density (Pf) of the nematode was 10.3 eggs+juveniles+immature females and eggs/cm3 soil and occurred at Pi=1 juvenile+young female/cm3 soil.