Tl-201 SPECT in a 33-year-old man with a pineocytoma showed increased uptake with rapid washout. Tc-99m MIBI SPECT showed diffuse, increased uptake with marked retention. Histologically, this tumor was negative for P-glycoprotein. It is thought that MIBI is effluxed by P-glycoprotein. Findings on Tc-99m MIBI imaging might be a result of defects of P-glycoprotein.