We agree with Levy et al.'s conclusion (Schizophrenia Bulletin, Vol. 19, No. 3, 1993) that global quantitative measures of eye tracking dysfunction (ETD) have an important role in studies of ETD in schizophrenia. We clarify some misunderstandings of our own work contained in their review. In particular, an explanation is presented of how we computed a fit of our data to their Mendelian latent structure model, when testing for a fit to their hypothesis of essential genetic homogeneity. We also point out that our mixture analyses, as with our reported abnormality rates obtained by using cutting scores, are not in agreement with their reported rates of ETD in schizophrenia.