The reproduction of Radopholus similis isolates from different origins and hosts was compared in carrot disk cultures at different temperatures. At 15degreesC, only the isolates collected from ornamental plants in Europe reproduced. The greatest fecundity was observed at 25degreesC. The reproduction factor (final population/initial population: Pf/Pi) ranked the isolates in similar order for four of the temperatures studied ( 15, 20, 25 and 30degreesC). When carrot discs at 28degreesC were inoculated with single females of isolates selected from those with different reproductive factors, this ranking was confirmed. This suggests that reproduction is controlled by intrinsic isolate characteristics which are not influenced by temperature. Isolates with most reproduction had a greater percentage of reproductive females than isolates with less reproduction, associated with a high ratio of females : males and a high proportion of females in the total production. The mean offspring per productive female was similar for high and low reproducing isolates.