A new adsorption equation,viz.,\(a = \frac{{\rm A}}{{1 + \alpha \cdot e^{ - k^c } }}\) has been derived for those cases of adsorption where the previously adsorbed molecules facilitate the adsorption of more molecules striking the surface of the adsorbent. This equation fits in well with the adsorption data yielding the familiar S-shaped curves and should find extensive application.