Routine laboratory testing of 710 bean seed lots from various origins forPseudomonas syringae pv. phaseolicola (Psp) with immunofluorescence microscopy (IF) showed that 27.5% of the seed lots (five subsamples of 1000 seeds tested per sample) contained two or more IF-positive cells in a total of 500 microscope fields (magnification 500×). Simultaneously performed dilution-platings of IF-positive subsamples on King's medium B confirmed presence of Psp for one-third of these IF-positive seed lots. The ‘grey area’ of disagreement between both laboratory tests was studied by comparison of test data and by field trials.