An assessment of the completeness and reliability of data from a survey of the physical characteristics of residential buildings, the properties on which they were located, and the immediate neighborhoods of a sample of 4,413 residential properties in Brown County, Wisconsin (Site 1 of the Housing Assistance Supply Experiment). Outcomes of survey attempts were accounted for, and tests were conducted for nonresponse bias. Checks were also made for response errors and anomalies in the survey instrument or in evaluator training or field procedures. Nonresponse bias, resulting from the inaccessibility of some interior public areas, exists for evaluations of the features of such areas among urban rental properties with two to four units. And evaluators' ratings of the quality or condition of various features of buildings were not consistently reproduced by other evaluators, operating independently. Users of the data should limit their comparisons of such ratings for individual buildings; unless the ratings differ by at least two intervals on a 4- or 5-point scale, it cannot be reliably concluded that the buildings in fact differ.