In 38 females, aged 21.3 ± 1.8 years (mean ± SD) and 22 males, aged 21.6 ± 2.0 years, total body water (TBW) was assessed by bioelectrical impedance at a frequency of 100 kHz (Z₁₀₀), and extracellular water (ECW) was assessed at a frequency of 1 (Z₁) or 5 kHz (Z₅). Impedance ratios of low frequencies (Z₁ or Z₅) to high frequency (Z₁₀₀) were calculated as indicators of body water distribution. Furthermore, changes in body water distribution during the menstrual cycle were assessed in 16 females, aged 22.1 ± 1.7 years, divided into subjects using or not using oral contraceptives. In general, the ratio ECW to TBW was lower in males compared to females, which was reflected in the ratios Z₁/Z₁₀₀ and Z₅/Z₁₀₀·However, the ratio Z₅/Z₁₀₀ reflected this difference less clear, probably because at 5 kHz the current partly passes the cell membranes. Weight changes during the menstrual cycle are generally accepted to be due to a retention of ECW. The ratio Z₅/Z₁₀₀ and the ratios Z₁/Z₁₀₀and Z₅/Z₁₀₀ for those subjects not using oral contraceptives differed significantly between day with minimal and day with maximal weight. A negative correlation was found between weight change, still considering day with minimal and day with maximal weight, and change in impedance at 5 and 50 kHz for subjects not using oral contraceptives. It is concluded that differences in body water distribution are reflected by low-to-high impedance ratios.