1. The metabolism of autologous 131I-labelled IgG was studied in five patients after renal homotransplantation. Two patients had received grafts from related living donors and three from cadavers and all grafts were functioning. All five patients were on immunosuppressive therapy with prednisone and azathioprine. No episodes of rejection occurred during the study.
2. One patient had serum concentrations of IgG and IgA and IgM below normal; one had isolated IgM deficiency; one had isolated IgA deficiency; and two had increased serum IgM concentrations.
3. Plasma volume and distribution ratio were normal in all five patients; the plasma IgG pool was normal in four and significantly decreased in one. Fractional turnover rate was normal in four and increased in one; the plasma half life was normal in three and shortened in two.
4. The IgG synthesis rate was normal in two, at the lower limit of the normal range in two and decreased in one. There was no obvious correlation with the age of the patient, the dosage of prednisone or azathioprine, the incidence of infection, the survival and function of the graft or serum immunoglobulin concentrations.