Flow cytometry (FCM) technique was applied to rapid determination of cell number of Lactococcus garvieae. An antiserum against L. garvieae was prepared and its immunological property was examined. The present antibody would recognize some epitopes of L. garvieae with a high specificity. The optimum conditions for the FCM assay were as follows: discriminate value, 60; dilution ratio of the antiserum, 1.0 x 10(4). Calibration curve for L. garvieae cells was linear, in the range of 2.4 x 10(4)-1.5 x 10(7) cells/mL. The detection of L, garvieae in cell suspensions contaminated with Escherichia coli was carried out. A good correlation was observed in the range of 20-90% for the mixing ratio of L. garvieae. One FCM assay could be completed within 2 min, and the total assay time, including the preparation of bacterial sample, was within 3 h.