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The effects of pressure and temperature variations on the determination of water-vapor densities from ruby-laser radar returns are considered. At the center of the 6943.8-Å water-vapor line, the thermal dependence of the absorption cross section is almost negligible while the pressure dependence is not. Water-vapor densities should be deduced from the line strength, which is independent of pressure, rather than the absorption coefficient as has been done previously. The 6943.8-Å line strength and line width were measured over a fixed-length atmospheric path using a ruby laser as 0.17 cm−1 g−1 cm2 and 0.098 cm−1 bar−1 (295 K), respectively, with standard error estimates of 16 and 9%.