A PCR-based detection system for Pseudomonas anguilliseptica was evaluated. The primer combination PAF-PAR (forward primer PAF = 5'-GACCTCGCCATTA-3', reverse primer PAR = 5'-CTCAGCAGTTTTGAAAG-3') gave a unique and specific amplification product of 439 bp at an annealing temperature of 46 degrees C with all the P. anguilliseptica isolates and strains (n = 56) but no amplification products were observed with any other Pseudomonas species or phylogenetically related bacteria tested. The PCR assay had a detection limit of 170 to 200 cells per PCR tube, which was improved 8-fold when the PCR amplification product was used as a nonradioacfive probe in blotting hybridization experiments. The PCR assay allowed the specific and reliable detection of P. anguilliseptica within 8 h, compared with up to 10 d required for its isolation and further characterization by conventional microbiological approaches. Clinical isolates of P. anguilliseptica recovered from several winter disease (WD) outbreaks diagnosed in sea bream Sparus aurata in Spain and Portugal between 1996 and 2001 were characterized by pulse field-gel electrophoresis (PFGE) macrorestriction analysis. The 54 clinical isolates analyzed were included in 4 different pulsotypes. Pulsotypes B and C represented 54 and 25% of the isolates, respectively, and were responsible for most of the WD outbreaks diagnosed in Spain between 1996 and 2001. The implication of asymptomatic infected carriers in the dissemination and spread of WD is discussed.