AbstractExplants of pig kidney cortex and medulla release a catabolin‐like factor (CLF). The CLF of both kidney cortex and medulla can be precipitated with ammonium sulphate, mainly in the 60–95 per cent fraction. By gel chromatography the kidney CLF showed a major active fraction at a molecular weight of around 22 500.Whole glomeruli and dissociated glomerular cells in culture also released into the medium a CLF that could be bioassayed in live cartilage but displayed no effect on dead cartilage. The possible role of such a local hormone is discus