Urinary levels of β(2)-microglobulin in healthy non-pregnant and pregnant women were determined. None of the women showed urinary protein, urinary glucose or urobilinogen. The results were: 1. The actual amount of urinary β(2)-microglobulin, the amount corrected for specific gravity (1.024), and β(2)-microglobulin / creatinine ratios were significantly higher in pregnant women than in non pregnant women. 2. The logarithms of corrected urinary β(2)-microglobulin levels were significantly higher in pregnant women than in non-pregnant women.