In prior work, a 50 kDa protein was purified to homogeneity from rat urine. This protein reduces food intake when injected into rats and is the only natural substance other than satietin known to be effective for long (24 hour) time periods and which does not make animals ill. However, when attempts were made to repeat the purification, contamination appeared in the 50 kDa fraction. The present contribution documents successful reisolation of the 50 kDa anorexigen by an improved method. Reisolation involved Cibacron blue-Sepharose, DEAE-Sephacel and Sephacryl S-200 chromatography, and SDS disc preparatory electrophoresis. The reisolated 50 kDa anorexigen contains no detectable carbohydrate. Partially purified preparations of the 50 kDa anorexigen were fragmented with trypsin and proteinase K without loss of anorexigenic activity. It is concluded that the 50 kDa anorexigen may be reproducibly purified to homogeneity and may contain within its amino acid sequence a peptide which is the basis of its anorexigenic activity.