During the 1991/92 growing season, two field experiments were carried out at the Carillanca Regional Research Center (Temuco, Chile), in order to evaluate the critical period of weed inteñerence on seed yield of dry peas cv. Progreta and lentil cv. Araucana-INIA. Both cultivars were kept with and without weed for different periods since plant emergence. Treatments were arranged in a split plot design with main plot being at two row spacings (17 and 34 cm) and subplots, being the weedy and weed-free periods (0, 15, 30, 45, 60, 75 days, until harvest). Reduction of row spacing from 34 to 17 cm did not increase weed competition ability either in peas or in lentil. The critical period of interference (PCI) in peas occurred from the 4th vegetative node and beginning of flowering, during 49 days. In lentil, the PCI occurred from the 4th and 6th vegetative node until full flowering lasting 71 days.