The effect on glomerular filtration rate (GFR), renal plasma flow (RPF) and excretion of albumin and beta-2-microglobulin in the urine after a high oral protein or amino acid load was investigated in young healthy males. After both test meals an increase in GFR of 10%, and in RPF of about 9-18%, was seen. The filtration fraction and albumin excretion rates were unchanged. The increase in GFR was significant from 20 to 60 min after intake of meat and remained elevated for more than 2 h. After the meat meal, a decrease in renal vascular resistance and an increase in S-creatinine, S-phosphate, S-carbamide and beta-2-microglobulin excretion rates was seen, but not after the amino acid load. During the experiments a gradual decrease in S-protein was noted. We conclude that the increase in RPF and GFR caused by intake of protein or amino acids in short-term experiments is not associated with impaired permselective properties of the glomerular membrane expressed in the albumin excretion rate.