Different forms of GH present in freshly prepared homogenates of chicken pituitary were analysed by high-performance gel permeation chromatography and by immunoblotting following sodium dodecylsulphate polyacrylamide gel electrophoresis, non-denaturing polyacrylamide gel electrophoresis and isoelectric focussing. Chicken GH was found to occur mainly in a monomeric form with a relative molecular mass of 23 500 together with small amounts of interchain disulphide-linked oligomers. No evidence was obtained for proteolytically modified forms of GH nor for a form analogous to the 20K variant of human GH. Isoelectric focussing resolved ten distinct charge variants of chicken GH with isoelectric points between 8·45 and 6·0. The predominant charge variant (pI = 7·85) was present in pituitaries of birds of both sexes at all ages examined (3–114 days) whereas the more acidic forms were not apparent until after day 13. These findings indicate that the chicken pituitary contains different forms of GH, some of which may be developmentally regulated.