We found inconsistency in reports of extracted nmatodes between two nematode diagnostic laboratories. Each laboratory analyzed 200 matched soil and 200 matched root samples. Agreement in detection and nondetection for three nematode species in soil was less than 85%, and in roots agreement was greater than 85% for one of the three species. Relationships were not found to support consistency between matched samples in which the same nematode was detected by both laboratories. An explanation, in part, for the inconsistency may lie in the dilution and counting procedure of the extraction process. A first approximation to a model for minimizing counting errors suggests that, when dilution is required for the counting of nematodes, differing dilutions should be used, and that, if a single sample is taken, about 840 nematodes should be present in the sample. However, the same precision can be achieved with about 170 nematodes per sample if four samples are counted and averaged.
