In winter of 2003 and 2004, severe leaf and stem necrosis symptoms were observed on watermelon (Citrullus lanatus) and melon (Cucumis melo) seedlings in two commercial nurseries at Adana, Turkey. The first symptoms, water-soaked lesions, were observed on the cotyledons. Small, dark brown and angular leaf spots on the true leaves and necrosis on the stem, were observed at later stages of the disease. Fluorescent, yellowish mucoid, aerobic, rod-shaped, Gram-, oxidase-, levan-, and arginin dihydrolase-negative and catalase-, pectolytic- and hypersensitive reaction-positive strains were isolated from diseased plant samples. The isolated strains were identical to the original strain, Pseudomonas viridiflava GSPB 1685 (obtained from Georg-August University Gottingen, Germany). In pathogenicity tests, all seventeen representative strains were pathogenic on watermelon and melon seedlings. Traditional methods and fatty acid analysis (Ataturk University, Erzurum, Turkey) identified the strains as P viridiflava with similarity indices ranging from 59 to 92%. The isolates had 12 fatty acids that included 10:0 3OH, 12:0, 12:0 2OH, 12:0 3OH, Sum in Feature 3 (16:1 w7c or 15 iso 2OH), 16:0,17:0 ISO, 17:1 w8c, 17:0 CYCLO, 17:0, 18: 1 w7c, and 18:0. The strains were divided into two different groups according to cluster analysis of fatty acids. However, no correlation was found between watermelon and melon strains isolated. Stem necrosis of tomato caused by P viridiflava has been reported previously in Turkey but this is the first outbreak on melon and watermelon in Turkey.