In 1982, the bipyridilium herbicides diquat [6,7-dihydrodipyrido (1,2- :2;i-c) pyrazinediium ion] at 0.56, 1.12 and 2.24 kg ai/ha, and paraquat [1, 1-dimethyl-4,4' -bipyridinium ion] at 2.24 kg ai/ha were evaluated for postemergence control of weeds in pumpkin cv. Borinquen (Cucurbita moschata (Duchesne) Poir). The experiment was established in Fraternidad clay soil, a Vertisol at the Lajas Substation, Agricultural Experiment Station. No statistical differences (P=0.05) in yield were detected among the hand-weeded plots (25,580 kg/ha), diquat treated plots (23,296 kg/ha), and paraquat treated plots (27,341 kg/ha). Significant differences in plot yield were observed among paraquat 2.24 kg rate treatment, diquat at the lower rates, and the non-weeded plots. Yields were 0.56 kg diquat (17,172 kg/ha), 1.12 kg diquat (19,551 kg), and non weeded check (10,243 kg/ha). All rates of herbicides provided 100% control of Ipomoea tillacea L.; the higher rates also controlled over 85% Euphorbia heterophylla. Control of grass weeds was inefficient (10% or less) with diquat sprays 1 month after the second herbicide application. Nevertheless, diquat seems to be a promising candidate herbicide for postemergence weed control in pumpkin since it efficiently controlled broad leaf weeds with less toxic effect on applicators than paraquat.