Forty rats are trained to run a maze. Half are food deprived to 85% of the weight they attain when allowed to eat as much as they like, half are food deprived to 90% of this weight. Half of each of these two groups learn the maze in the presence of odours thought attractive to rats, half in the presence of normal laboratory smells. The time taken to run the maze at the end of 10 days training is measured. It is hypothesised that the hungrier rats will be faster at completing the maze. This increase in speed is expected to be more marked in the presence of attractive odours.