Small, gamma-sensitive, cadmium-telluride [CdTe(C1)] detectors are evaluated for biotelemetry of the local clearance of an injected radioactive depot in tissue. The lateral displacement dependence and depth dependence are determined with 99mTc as radiation source. Perspex is used as attenuation and scattering medium. With 133Xe injected into subcutaneous tissue the effect of a geometrical adjustment of the CdTe(C1) detector prior to measurement is studied. Examples of 133Xe disappearance curves are shown during rest and ergometry bicycling.