Abstract –Four patients with herediatry hyperplasia of the gingiva were studies. Bipsy samples of gingival tissue contained subepithelial loose connective tissue with thick rounded fibroblasts or dense collagen‐rich connective tissue with thin fibroblasts, which appeared to be inactive These two types of fibroblasts differed in electron microscopy. alcian blue‐staining of intercellular material in various. MgCL2concentrations was similar in hyperplastic and control samples. Collagen from the hyperplatic gngiva appeared to be more mature than normal, based onthe presence of stable, nonreducible cross lines. an investigation of growth harmone secretion and treatment trial suggested that the growth retardation observed in earlier studies was due to normal variation in growth rates (in one patient) to hypopituitarism associated with birth in breeth present