Increased oxalic acid absorption, hyperoxaluria and oxalatelithiasis are found in many gastroenterological diseases. All persons receive 370 kBq 14C-oxalic acid for the measurement of oxalic acid absorption. The absorbed and in the urine excreted 14C-activities are measured with a scintillation spectrophotometer and scintillator composed of 2,5-diphenyloxazole(POP), 1,4-bis-(4-methyl-5-phenyl-2-oxazolyl)benzene (dimethyl-POPOP), naphthalene, toluene and ethyleneglycol monomethylether. Normal values of oxalic acid absorption are means +/- S = 7.17 +/- 1.87%/24 h (n = 40).