Sclerotinia head rot, caused by Sclerotinia sclerotiorum (Lib.) de Bary, is a major disease in sunflower (Helianthus annuus L.). Development of hybrids with adequate genetic resistance is necessary to reduce yield losses. The objective of this study was to find an effective technique of inoculating sunflower heads with Sclerotinia sclerotiorum for screening and identifying resistant and susceptible genotypes. A factorial experiment was conducted to evaluate the effectiveness of different inoculation procedures. The factors were bag color, water treatment, inoculum type, and rate of inoculation. Based on the results of this study, the inoculation procedure recommended to sunflower researchers who wish to screen lines or hybrids for Sclerotinia head rot resistance is spraying the heads at the beginning of flowering with 5 cm3 of a suspension of ascospores containing 5000 ascospores per milliliter and covering the heads with brown paper bags immediately after inoculation. Application of additional water is not needed. Measurements of infection could begin as early as 35 days after inoculation