Southern stem rot, caused by the soilborne fungus Sclerotium rolfsii, is a major disease of peanut (A. hypogaea) in the U.S. Advanced lines from the Univ. of Florida peanut breeding program were evaluated in field tests at the Marianna North Florida Res. and Educ. Center for resistance to stem rot. Breeding lines and cultivars were evaluated in irrigated field studies in 1999 to 2001. Plants were inoculated at 55 to 65 d after planting with aggressive isolates of S. rolfsii that were grown on grain-based (oats, corn) medium in the laboratory. Entries planted in three tests were grouped based on maturity (early, medium, late). Additional split-plot field tests were conducted to compare inoculated vs. uninoculated plants of selected lines. Late-maturing entries consistently showed the highest levels of resistance to stem rot and greatest pod yields. In general, early and medium entries had similar yields, but some medium-maturing entries had greater pod yields and better disease resistance than any of the early genotypes. The mean pod yields for the early, medium and late maturity groups were 2697, 2780, and 4301 kg/ha, respectively. The mean disease ratings on a 1–10 scale (1 ≤ 10% disease; 10 ≥ 90% of plants dead or dying) were 4.6, 4.4, and 3.4, for the early, medium, and late maturity groups, respectively. The mean yield loss to stem rot in the split-plot test was 706 kg/ha. New cultivars with resistance to stem rot were released from the Florida Agric. Exp. Sta. in 2002 and 2003 from material reported in these tests.