This study reports the adaptation of an electronic particle-counting method for the enumeration of T cell and B cell rosettes of human lymphocytes. This method and the conventional hemocytometer method were compared in parallel on seventeen T cell and seven B cell rosette enumerations in a blind study design. All data were analyzed for statistical significance; correlation coefficents were calculated. There was significant agreement between both methods for T cells at p less than 0.001 (mean particle counter 80.6% +/-11.3 mean hemocytometer 76.7+/-8.2%) and for the B cells at p less than 0.002 (mean particle counter 22.5+/-9.7, mean hemocytometer 23.4+/-5.12). These results demonstrate that the electronic particle counter is useful as a rapid, convenient, semi-automated method for the enumeration of T cell and B cell rosettes.