A new technique of technetium labeling using stannous pyrophosphate instead of stannous chloride as reducing agent for pertechnetate has been applied to red blood cells and bleomycin. Results are so encouraging that this technique could be extended to other compounds capable of forming stable complexes with reduced technetium. No saline washes of red cells are necessary before or after the addition of pertechnetate. No purification step is performed after labeling of bleomycin.