Transgenic cotton (Gossypium hirsutum L.) with the Bollgard (BG) genes, the Roundup Ready (RR) gene, or both (BG/RR) has been grown commercially since 1996, 1997, and 1997, respectively. Because genes used in the past for one purpose have often had unforeseen effects on nontargeted traits, these experiments were conducted with cotton across several genetic backgrounds to determine whether the BG, RR, and BG/RR genes have an effect on lint yield, two measures of lint percentage, and five fiber quality traits. Replicated field trials were conducted as if for conventional (i.e., nontransgenic) cotton at two irrigated locations in Oklahoma over 2 years. The BG genes were stable for lint yield across genetic backgrounds, but the RR gene was not. BG significantly increased lint yield across genetic backgrounds in three of four experiments (from 6.7 to 11.8%) with an average of 6.2% over all four. In one background, RR decreased lint yield in two experiments (from -7.3 to -22.2%), but increased it (12.7%) in another. RR increased yield (10.5%) in another background in one experiment, but had no influence in two other backgrounds. Clearly, RR can reduce lint yield in some backgrounds in some environments. BG/RR increased lint yield by 2.5 and 16.8% in two backgrounds over four experiments. In BG/RR, higher yields associated with BG apparently overcame the occasional deficits associated with RR by 7.2 to 9.6%. BG/RR increased lint yield by 8.6 and 9.0% above RR in two backgrounds over four experiments. In another background, the increase was not significant. BG/RR (like BG) often increased lint yield in individual experiments, but caused no significant yield reductions. BG reduced picked lint percentage (-0.7%) and fiber fineness (-0.1 to -0.2 micronaire units). RR increased pulled lint percentage (0.8%), had a neutral or negative effect (-0.3 to -1.0 mm) on fiber length, and showed a neutral or positive effect (0.2 to 0.4 units) on fineness. BG/RR reduced fiber length (-0.3 to -0.8 mm), length uniformity (- 0.7 to -1.1%), strength (-8.9 kN m kg-1), and elongation (-0.2 to -0.4%), but it increased fineness (0.1 units). Relative to RR, BG/RR had a neutral or negative influence on picked lint percentage (as much as -1.2%), fiber length uniformity (-0.1 to - 0.7%), fineness (-0.4 units), and strength (-10.3 kN m kg-1). Traits not mentioned above were mixed in the direction of their response or were too small to be of statistical significance or practical value.