We evaluated whether "sweetness" increases hunger. Groups of 10 male and 10 female subjects chewed a gum base containing one of four concentrations of aspartame (0.05%, 0.3%, 0.5%, or 1.0%) for 15 min. Relative to groups given nothing or unsweetened gum base to chew, groups given the sweetened gum bases increased hunger ratings, but not in a manner monotonically related to aspartame concentration. The most effective aspartame concentration to increase hunger was 0.3% for females and 0.5% for males. The highest aspartame concentrations had a time-dependent, biphasic effect on appetite, producing a transient decrease followed by a sustained increase in hunger ratings. Thus, the concentration of the sweetener, the sex of the subject and the time after chewing, were all important determinants of whether "sweetness" increased hunger.