A monoclonal antibody (A7) was produced which recognizes an oncofetal antigen expressed on glloblastoma multiforme cells, fetal brain, fetal kidney, but not adult tissues. Radioimmunoprecipitates of Zwittergent 3–14 solubilized glioblastoma cells identified a single band at 138 kDa on 8% polyacrylamide sodium dodecylsulfate gels. Distribution studies of A7 in mice demonstrated a tri-phasic serum clearance oft1/2α= 2.1 h,t1/2β= 16.7 h andt1/2γ= 151.1 h. Tumor localization studies using the U-87 MG xenograft demonstrated the ability of A7 to localize with a tumor: blood ratio of 1.294 ± 0.094 as compared with 0.293 ± 0.051 for control antibody AC. A7 does not damage cell membranes and is not internalized when bound to reactive tumor cells.