The urinary excretion of IR-HGH was studied in patients with various diseases. The urine of patients with pituitary dwarfism, acromegaly, renal hypoplasia, diabetes mellitus, hepatitis, nephrosis, gout and after surgery and that of healthy adults was collected for 24 hours in a cold room. An aliquot of the urine was dialyzed by collodion bag, and IR-HGH was measured by radioimmunoassay with the double antibody technique. Patients with acromegaly, renal hypoplasia and after surgery showed high urinary IR-HGH values compared with healthy subjects, but in patients with pituitary dwarfism, the urinary IR-HGH values were negligible.To prove the purity, identity, molecular weight and bioactivity of these urinary IR-HGH values, another experiment was performed. Urine was collected and concentrated 1000 or 2000 times by diaflow membrane ultrafiltration. The material in the concentrated urine was then separated into two fractions (A, B) by gel filtration on a Sephadex G 100 column. A part of fraction A (component) was identified with extracted pituitary HGH (ep-HGH) by methylcellulose acetate electrophoresis, thin layer chromatography (TLC) and disc electrophoresis. Fraction B, however, had not the component corresponding to ep-HGH. Although disc electrophoresis showed the highest sensitivity. TLC easily collected the sample. On the other hand, brown-white powder which was obtained by Raben's method from concentrated and lyophilized urine was also identified with ep-HGH by TLC.Fraction (A, B) and the material corresponding to ep-HGH on TLC were injected into hypophysectomized male rats to determine the bioactivity of these substances.For an estimation of molecular weight, the latter was further filtrated on a Sephadex G 100 column.The following results were obtained : 1) Urinary IR-HGH was separated into four components by gel filtration on a Sephadex G 100 column.2) Only one of these IR-HGH components was coincident with ep-HGH.3) The material corresponding to ep-HGH on TLC was eluted again by gel filtration on a Sephadex G 100 column. Kav of 0.39-0.43 was measured, and this result suggested that the molecular weight would be 20,000-30,000.4) The material corresponding to ep-HGH on TLC and fraction A had both bioactivity and immunoreactivity. On the other hand, fraction B had no bioactivity but had immunoreactivity.From these results, it was suggested that IR-HGH is not a single material, and materials containing both intact HGH and its non-bioactive fragments are excreted in urine.