A new analytical formulation of the absorption and desorption of a nonreactive gas across an infinite planar gas-liquid phase boundary is presented. The solution describes diffusive transport in the gas and liquid phases and the kinetic resistance at the phase boundary according to the Hertz-Knudsen equation. The expressions allow straightforward examination of various kinetic regimes and the calculation of their characteristic times. The violation of Henry’s law during the uptake is illustrated by derivation of simple formulas for the concentrations in both phases close to the surface. Also, expressions for the time-averaged uptake coefficient (<(gamma)over bar>) are presented.