The reproductive fitness of three Pratylenchus coffeae populations (Honduras, Ghana and Vietnam) and three Radopholus similis populations (Costa Rica, Cuba and Ghana) on carrot disks was studied as a function of time and inoculum densities. In the first study, the reproductive fitness of the isolates was followed during 11 weeks for P. coffeae and during 7 weeks for R. similis. All the populations increased with time. No distinction could be found in the maximum growth rate of the Pratylenchus populations. The R. similis population from Cuba had a higher maximum growth rate than those from Ghana and Costa Rica. All the Radopholus populations showed a faster multiplication than P. coffeae. In the second study, the influence of the inoculum density on the reproductive fitness was determined for the six populations. The differences in reproduction ratios confirmed the results of the first study.