The results of pilot rodent studies with aspartame are discussed. It is suggested that its use as an artificial sweetener for soft drinks may cause human neurochemical changes that could have functional or behavioral consequences. The results show that, if aspartame-containing beverages are consumed with normal dietary carbohydrates, the effect of aspartame on brain composition is enhanced. Carbohydrates cause an insulin-mediated decrease in branched-chain amino acid levels that compete with phenylalanine and tyrosine across the blood-brain barrier. The results of 1 experiment showed that aspartame almost doubled rat brain phenylalanine levels, an effect which redoubled if carbohydrate also was consumed. The aspartame dose used in the study was consistent with the amount of aspartame an 8-year-old child might consume in soft drinks on a hot afternoon. (wz)