This study was conducted in Eskisehir during the 2004-05 and 2005-06 growing seasons, and aimed to evaluate the response of six bread wheat varieties to rainfed and irrigated conditions in terms of grain yield, heading date, plant height and position weight variation (PWV). Of the six varieties tested, three (Sultan, Yildiz, Bezostaja) are drought-sensitive cultivars and three (Gerek, Altay, Sonmez) are drought-tolerant cultivars. Spikes from each variety were divided into five spikelet groups in order to study the effect of spikelet position upon grain weight (S1, S2, S3, S4 and S5, with S1 the spikelet closest to the base). This study focused on position weight variation (PWV) in order to better understand how 1000-kernel weight is affected by spikelet position under both rainfed and irrigated conditions and thus gains a better understanding of wheat resistance to drought. Linear increases in grain yield, heading date and plant height were observed in response to irrigated conditions, whereas a linear increase in PWV was observed in response to rainfed conditions for both seasons. Grain yield was negatively associated with heading date (r=-0.746). PWV was positively associated with grain yield and negatively associated with heading date (p<0.01; r=0.804 and r=-0.860, respectively). The observed differences in grain weight between spikelet positions have important implications for drought tolerance in wheat and can be used as a new parameter for predicting drought tolerance.