1. The growth of established grasses-Kentucky bluegrass, red fescue, and redtop-growing in mixed stand with a rather heavy weed infestation of narrow-leaved plantain was measured by weighing clippings periodically during the summer following spring application of 2,4-dichlorophenoxyacetic acid spray mixtures to eradicate the weeds. The effect on growth of grass from adding urea as a fertilizer and Fermate as a fungicide to the herbicidal sprays containing the ammonium salt of the acid was also studied. Comparisons were made with weedy control plots from which the clippings of weeds and grass were sorted and weighed separately. 2. Immediately following application of the sprays (1000 p.p.m. of the acid or 1500 p.p.m. of the ammonium salt) the rate of growth of grass was significantly reduced for a short time, 10 days to 2 weeks. The reduction in most instances was greater than that caused by the competition of a rather dense stand of weeds. However, the grass soon recovered from the spray treatment and, without the competing effect of the weeds, produced 15-80% more leaf growth on the sprayed than on the weedy unsprayed plots. 3. Application in late August of a spray mixture composed of 1500 p.p.m. of the ammonium salt of the acid and urea sufficient to apply 60 lb. per acre caused the grass to become much greener in color within a few days. The urea apparently had no adverse effect on the selective herbicidal properties of the acid salt, so that, as a result of weed elimination and fertilization, the grass in the sprayed plots produced 40-131% more growth in the 2-month period following treatment than did that in the unsprayed plots. 4. Under conditions of the experiments no burning or other injury to the grass was obtained with the herbicidal sprays to which urea equivalent to an application of 60 lb. per acre was added. However, when the urea content was increased to the equivalent of an application of either 90 or 120 lb. per acre, the grass was severely injured but recovered by the end of 1 month following treatment. 5. Although no attempt was made to measure the fungicidal properties of Fermate when applied in spray mixture with 1500 p.p.m. of the ammonium salt of the acid, it is of interest that Fermate at the rate of 2 lb. per 100 gallons in the mixture had no apparent effect on the herbicidal action of the spray.