Acid extracts of porcine pancreas acetone powders (but not of other tissues) have been shown to contain material which will react firstly in a radioimmunoassay for beta-endorphin, and secondly, compete with 3H-Naloxone and 3H-enkephalinamide in the radio-receptor assay. This material had a molecular weight of approximately 7,000 as judged by both P-10 and G-50 exclusion chromatography, even in the presence of 4 M urea. The G-50 partially purified and desalted fraction demonstrated a dose-dependent analgesia in mice and also influenced mouse behavior in vivo in a manner analogous to that produced by synthetic human beta-endorphin.