Nine breeding lines originally selected by a Pythium petri plate assay, were tested in a field naturally infested with P. ultimum. A susceptible variety, Paymaster (PM) 2326RR was included in the test, without chemical protection against P. ultimum and Rhizoctonia solani (-) and with chemical protection (+). All other entries, including PM 2326RR-, were treated only with Captan before planting. All seed was inoculated with R. solani (grown on oat grains) at planting. Treatments were arranged in a RCBD with four replications. At 28 days after planting, 8 of the 9 breeding lines had significantly (P = 0.05) better stands than PM 2326RR (-). All nine breeding lines had stands which were not significantly different than PM 2326RR (+). Five of the breeding lines had a slower rate of emergence at 14 days after planting than PM 2326RR (-), and one line (G52) only had 31 % of the stand it would ultimately achieve. PM 2326RR (-) had significantly poorer yields than PM 2326RR (+) and seven of the breeding lines. However, many of the breeding lines had poorer lint quality, particularly in the area of fiber strength or length than PM 2326RR. The Pythium petri plate assay appears to be an efficient method to identify cotton lines with enhaced disease resistance to P. ultimum and R. solani.