A programmable apparatus with underlighting, the EthoStudio apparatus, is described; this provides highprecision tracking of the movement of an animal of any color in a Morris water maze (MWM). The apparatus was based on the use of transmitted light (underlighting). The programming provided for assessment of a large number of learning measures. We report here studies of the statistical features of three of the most widely used measures: the latent period of finding the platform, the path followed, and the sum of distances to the center of the platform. The path followed showed better statistical features than other measures. The effects of the C1473G polymorphism in the gene for the key serotonin synthesis enzyme tryptophan hydroxylase 2 on the learning of mice in the MWM were studied. Mice of the unique congenic strains B6-1473C and B6-1473G, with different alleles at the C1473G polymorphism, did not show any relationship between learning ability and genetically determined tryptophan hydroxylase 2 activity in the brain.