Culture of the Gray Zucchini (GZ) variety of summer squash in northwestern Mexico during the fall is severely affected by a viral disease, which is apparently caused by squash leaf curl virus (SLQV). Resistance to this disease was introduced from local Cucurbita moschata landraces and uniform GZ-type lines and hybrids (GZLH) were developed. Crosses between lines were performed during Spring 1995. In the Fall, 21 GZLH plus the commercial materials PSR-59792, Raven, and GZ (usually included as a control) were studied. The commercial materials showed a higher degree of virus infection than GZLH. Four of the materials that showed symptoms of virus infection and one free of symptoms were tested for SLCV and all were positive for this virus. Eight GZLH had higher overall and 1× yields than GZ and nine and four GZLH were better than GZ for 2× and 3× yields, respectively. Number of stems varied from one to seven and stem and internode length had values from 42 to 145 cm and from 1.2 to 4.8 cm, respectively. These results were consistent with other similar studies previously reported.