Reniform (RN) nematodes, a parasitic pest to cotton occur in many fields of the Lower Rio Grande Valley of Texas. Cotton grown in these infested soils often appears unhealthy and produces poor yields. In 1992, a field study was conducted in RN-infested and fumigated experimental plots to determine the effects of the RN nematode on cotton and to ascertain if newly developed breeding lines possess greater levels of resistance or tolerance to the RN nematode than the public released resistance germplasm line La. RN 1032. Cotton grown in the RN-infested plots showed a longer period to first bloom and a reduction in plant growth, first harvest and total lint yield. Seven of the 10 breeding lines had greater plant growth rates, first harvest, and total lint yields compared to Stoneville 453 and La. RN 1032. In addition, when growth rates and lint yields were compared between the fumigated and RN plots, the improved breeding lines were less affected by the presence of RN nematodes. Results suggest that several of the breeding lines may have greater tolerance or resistance to RN nematodes.