Field experiments were conducted in 1982 and 1983 to screen 20 lines of safflower (Carthamus tinctorius L.) for resistance to head rot caused by Sclerotinia sclerotiorum (Lib.) de Bary. Plots were artificially infested with sclerotia of S. sclerotiorum at seeding and irrigated during the growing season to maintain adequate moisture for carpogenic germination of sclerotia and production of apothecia. The reaction of each line to S. sclerotiorum was similar for the 2 years. Severity of head rot varied significantly among the 20 lines tested, ranging from 6% for Lesaf 34C-OO to 62% for Gila in 1982 and from 0.3% for Lesaf 34C-OO to 31% for PCA in 1983. Level of resistance was not related to the level of maturity of the lines. Yield losses ranged from 81 kg/ha for Lesaf 34C-OO to 678 kg/ha for Gila in 1982 and from 14 kg/ha for Lesaf 34C-OO to 935 kg/ha for PCA in 1983. Healthy plants averaged 4.4% more oil in the seed than did the corresponding parental lines. This study has demonstrated the possibility of developing early maturing safflower lines resistance to sclerotinia head rot for production on the Canadian Prairies.Key words: Carthamus tinctorius, Sclerotinia sclerotiorum