Rats are used routinely for the discovery of new pharmaceuticals and for toxicology testing to fulfill regulatory requirements. In 1999, a survey showed that 80% of all rodents housed in toxicology studies were housed in wire-bottom cages. However, both the National Research Council and Association for the Assessment and Accreditation of Laboratory Animal Care, International, recommend housing rats in solid-bottom cages with bedding. In this study 2 groups of male Sprague Dawley rats were housed in the same room for 4 wk and provided the same food and water by the same husbandry staff person. The only variable in the study was the type of housing. One group was housed in solid-bottom polycarbonate cages with bedding and the other group in standard wire-bottom caging. Clinical pathology laboratory evaluations of complete blood count, serum chemistries, urinalysis, urine creatinine, urine corticosterone, blood coagulation, and hepatic cytochrome P450 isoenzyme mRNA levels were performed. No clinically relevant differences were found between the 2 groups for any of the laboratory data.