Experiments were conducted during the 2002 and 2003 growing season at Texas A and M Agricultural Research Farm near College Station, TX to determine the response of two germplasm lines derived from IS8525 (juicy midrib = IS8525J and dry midrib = IS8525D) to ergot infection. Ergot inoculation was conducted at different flowering stages with bagging versus non-bagging of inoculated panicles to determine the disease response of IS8525. On IS8525J, bagged panicles had mean ergot severity of 21.3% compared to 1.8% for non-bagged panicles. Mean ergot severity for bagged panicles for IS8525D was 3.9% and non-bagged was 1.0%. The stage of anthesis at the time of inoculation also affected the severity of the disease with the highest level of infection occurring when panicles were inoculated at 25% flowering. Ergot severity decreased at later flowering stages. Bagging of the inoculated panicles at the beginning of anthesis generally increased ergot severity on both lines. In both years, IS8525J was more susceptible to ergot than IS8525D. Male-sterile hybrids derived from crosses between the two IS8525 lines with A2Tx623 were evaluated in 2004 and found to be highly susceptible to ergot. These results suggest that the tolerance of IS8525 is due to floral morphological characteristics and the flowering pattern.