1 - An experiment to study the various modalities of the application of the herbicides diuron and trifluralin in cotton plantings was carried out in purple latosol soil, Chapadão series. The two herbicides were applied in various doses and at different times. The most common weeds in the trial area were capim pé-de-galinha (goosegrass), capim carrapicho (sandbur), capim colchão (crabgrass), beldroega (purslane), carraplcho de carneiro, and poaia. 2 - The effectiveness of diuron (1.60 kg/ha), applied pre-planting, was not increased by incorporation into the soil. The control of weeds was efficient, but the yield was inferior to that of plots without incorporation. Of the weeds that survived the treatment, a predominance of grass species was noted. Some of the cotton leaves turned yellow in plots that received this herbicide, but this chlorosis was temporary and the plants regained their normal color within a few weeks. The tolerance of cotton for the treatments did not appear to be affected by the method of application of the herbicides. The method of incorporation in pre-planting was not found to be more advantageous than the pre-emergence treatment. 3 - A reduction in the dosage of diuron (0.80 kg/ha) in pre-pianting, with subsequent incorporation into the soil, did not give adequate control of annual weeds. 4 - The application of trifluralin (1 kg/ha), incorporated in pre-planting, gave excellent control of grass weeds, but the dicotyledonous species were little affected. 5 - A combination of diuron (0.80 kg/ha) and trifluralin (0.5 kg/ha) appears to be practical. The application of trifluralin in pre-planting, incorporated into the soil, and of diuron in pre-emergence, increased considerably the area of control of both groups of weeds. This practice, using two herbicides, offers the following advantages; a) greater variety of weeds controlled; b) a lessening of the opportunity for chlorosis to appear in the cotton by the use of a smaller dosage of diuron; c) a reduced residual effect for the subsequent crops; d) the band application of two products and reduction in cost of applied material; e) the possibility of cultivating between rows without loss of efficiency of the incorporated product. 6 - The treatment with diuron (1.60 kg/ha) applied in pre-emergence was sufficiently effective in the control of broad leaf weeds, while control of grass species was less so. Slight symptoms of phytotoxicity were noted, but these were not sufficient to affect the yield and with further development of the crop they disappeared. The yield from herbicide-treated plots was greater than that from check plots which received manual hoeing.