A very quantitative, destructive-analysis procedure was devised for assaying the 3 2 P activity content of ''hot-wall'' angioplasty-balloon catheters. These sources, developed and under investigation by Radiance Medical Systems, Inc. (Irvine, CA), are intended for use in the prophylactic inhibition of restenosis following balloon angioplasty in heart-disease patients. The assay was based on performing a physicochemical digestion of the balloon catheter to extract the 3 2 P activity followed by liquid-scintillation (LS) spectrometry of the resultant solutions. Measurement-based corrections were applied for the residual activity remaining in the digested balloon debris and in all of the digestion apparatus. The LS spectrometry, with 3 H-standard efficiency tracing, utilized a previously-developed method for resolving the always-present 3 3 P impurity. Initial ionization current measurements on the sources prior to the destructive assays led to the establishment of calibration factors that can be used for subsequent non-destructive radionuclidic measurements on similar balloon-catheter sources.