This study compares owner's estimates of house value and professional appraisals for a sample of owner occupied single family and multifamily units in St. Louis. It confirms the findings of an earlier study by Kish and Lansing that: (1) the errors of estimate are quite large for individual properties, but, (2) the errors are largely offsetting for reasonably sized samples. In addition, the analysis indicates errors of estimate are systematically related to the socioeconomic characteristics of the owner-occupants and that knowledge of these biases can be used to improve the accuracy of both the individual and aggregate estimates of market value.