The background control data were compiled from rat developmental toxicity studies con-ducted at Toxicology Research Center, KRICT during the 1993-1999 period. These data were assembled in order to provide background in formation for the maternal and fetal data collected in 13 developmental toxicity studies using Sprague-Dawley rats. A total of 325 mated females were used in these studies during the seven-year period and overall pregnancy rate of these females was 93.8%. The present background control data included body weights, food consumption, hematological values, and organ weights of pregnant females, caesarean section data, and fetal examination data. These data can be used not only as a historical database for the meaningful interpretation of data from reproductive and developmental toxicity studies, but also as a contribution to biological characterization oj Sprague-Dawley rats.