Abstract: Environmental conditions conducive for leaf rust development were determined at Starkville, MS, during the 1991-92 and 1992-93 wheat growing seasons. Four wheat varieties, grown in a randomized complete block design and infected by natural inoculum, were rated weekly for leaf rust severity. The relationship of weekly maximum, minimum and average air temperatures, dew point, relative humidity, total rainfall, soil temperature, solar radiation and wind movement to leaf rust severity was determined by polynomial regression. Leaf rust severity for each of the varieties was different under differing environmental conditions. In 1992, the relationship between leaf rust severity and weekly air and soil temperatures and solar radiation was linear for most varieties. In 1992, significantly higher solar radiation and soil temperature, lower rainfall and less wind movement contributed to greater leaf rust severity compared to 1993. During two seasons neither quadratic nor qubic regression models fit the data well for most of the environmental parameters. During 1992 leaf rust development on all the four varieties in relation to weekly maximum, minimum and average air temperature and soil temperature was best explained by linear regression models. During 1993, the relationship of environmental condition to leaf rust severity recorded only on Pioneer varieties was best explained by linear regression models. The environmental conditions characterized for maximum leaf rust severity on four varieties included 25-27, 15-20, 21-23°C maxi, min, eve air temperatures and 85-90 percent relative humidity respectively.