Determination of protease-cleaved p-aminobenzoic acid (PABA) in serum after oral administration of N-benzoyl-L-tyrosyl-p-aminobenzoic acid (PABA-peptide) in children.

A modification of the urine PABA tet published by Imondi et al. is described. Ninety minutes after oral administration of PABA peptide, PABA was determined in serum. The average concentration in healthy children was 0.42 +/- 0.055 mg per 100 ml. Up to that time we recovered in the urine 66.1 +/- 6.1% of the substance previously administered. In the children with cystic fibrosis of the pancreas (CF) serum PABA concentrations were less than 0.1 mg per 100 ml. The infants under 2 months old also had clearly low serum concentrations, on average 0.29 +/- 0.06 mg per 100 ml, whereas the PABA concentrations in the older babies lay within the range for the older children (0.40 +/- 0.07 mg%).