The renal function of 32 malnourished Jamaican children was investigated by serial tests from admission until recovery. It has been established that in the malnourished as compared to the recovered children there are several functional renal lesions. There is a reduction in G.F.R. and R.P.F., and evidence of impaired tubular function as shown by aminoaciduria, occasional renal phosphaturia, impaired urinary concentration, and inability to excrete an acid load. There is no demonstrable difference in G.F.R. or R.P.F. between the edematous and non-edematous malnourished children. With recovery there was steady improvement in renal function. The etiology of these lesions may be related to the deficiencies of magnesium and potassium which are known to occur in malnourished children.