The relationship between urinary homovanillic acid (HVA), vanillylmandelic acid (VMA) and creatinine is investigated and reference ranges are constructed for HVA and VMA. A total of 769 urine samples were obtained from children and adults. The ratios HVA/creatinine and VMA/creatinine were highly correlated with creatinine concentration; hence, reference to creatinine was found to be an inappropriate adjustment for urinary dilution. An alternative method based upon linear regression is proposed. After allowing for differing levels of creatinine, HVA and VMA were found to be significantly correlated with age, height and weight for individuals aged less than 20 years. In those aged over 20 years, HVA was significantly correlated with weight and VMA with age. Differences between sexes were found in the levels of HVA and VMA, the exception being VMA in the over 20 age group. Reference ranges were constructed for HVA and VMA which are variously dependent upon creatinine, age, sex and weight.