Sources of resistance to Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and two local isolates of Cucumber mesaic virus (CMV) as the most destructive viruses to melon (Cucumis melo L.) fields in Iran were investigated. This study evaluated the resistance of melon germplasm under high disease pressure achieved with natural inoculations by indigenous aphid vector in the field, mechanical inoculations in the greenhouse, and then field comparison of resulting resistant and tolerant cultivars (cvs.) by natural and mechanical inoculations. The .majority of genotypes used in this study was open-pollinated (OP). Some selfed (S1) seeds and F1 hybrids were also included. The results indicated that most of the melon cvs were susceptible to both natural infection of cucurbit viruses in the field and mechanical inoculation in the greenhouse. However, melon cvs. 'Magotalena Vertbrod', 'Soski' and 'Bahramabadi' (OPs) were immune to ZYMV. Melon cvs. 'Galicum' (S1), 'Latifah-1' (S1), 'Tashkandi', (OP) and 'Khorasgani' (OP) were resistant to CMV and WMV under both greenhouse and field conditions. Melon cvs. 'Baghkomeh Lenjan', 'Oshtorjan', 'Lenjan', 'Firozan', 'Shahd-Shiraz', 'Ardian' and 'Latifah' (OPs) were tolerant considering both infection type and fruit yield reduction traits. Virulence of CMV#1, CMV#2, WMV and ZYMV differed significantly, where CMV#1 was the most virulent type having the highest mean of disease severity (3.59). The reassessment of the progenies of resistant and tolerant cvs with doubly infected plants in the field, provided evidence that the sources of resistance or tolerance found in the earlier field and greenhouse germplasm evaluations are heritable.