The features of the initial adsorption kinetics monitored at short adsorption times are investigated. It is shown that the concave character of the square-root dependence on time may be due to a combined effect of the rate of surface reaction and that of the transport from the bulb, to the surface. That effect causes the appearance of a certain subsurface region close to the surface, where the concentration of the sorbate is different from that in the bulk phase. For the purpose of illustration, the initial parts of the kinetic isotherms are analyzed for the RY/F-400 system already studied in our previous paper.