Vibrio parahaemolyticus strains isolated from different sources were assayed for their ability to produce a siderophore, vibrioferrin, under iron-limited growth conditions. The mean value } standard error of mean (μM vibrioferrin in spent culture supernatant/optical density at 660nm) was 832.3 } 66.9 for clinical isolates (n 44), which was significantly higher (P 0.01) than those for food isolates (461.0 } 66.5; n 37) and coastal isolates (378.8 } 37.2; n 26). This suggests that greater productivity of vibrioferrin by clinical isolates may be associated with a selective advantage for survival and proliferation under conditions of iron-limitation such as in the intestine.