In situ hybridization for Epo mRNA in a human hemangioblastoma using ³⁵S-labeled antisense and sense cRNA probes. Sections were counterstained with toluidine blue. Epo mRNA was detected in intervascular stromal cells. A-C, 100× original magnification; D-F, 400× original magnification; A and D, bright field illumination; B and E, dark field illumination; C and F, sense (control) hybridization and dark field illumination.