Over 10,000 plants of 643 breeding lines of squash and pumpkin were tested for resistance to four different viruses in the greenhouse. The breeding lines were classified as homozygous for resistance, segregating for resistance, or susceptible. On the basis of these tests, the best resistant lines were selected for planting in the field. They were evaluated there for resistance to viruses, powdery mildew, and cucumber beetles and for horticultural type.