The four currently available methods used for estimating urinary concentration were assessed. One hundred and fifty urine specimens were collected and 130 were measured. Twenty were excluded as they contained protein and/or glucose. The volume of 41 samples was inadequate for hydrometry. In urines not containing dissolved macromolecules, hydrometry, refractometry and osmolality reliably reflect the degree of concentration. Except at the extremes, the reagent strip on N-Multistix SG is not a reliable indicator of specific gravity. In a children's Hospital, one-third of urine specimens will be of insufficient volume for standard hydrometry.