Proceeding from the well-known infiltration model by Mein & Larson (1973) and several extensions, explicit equations for time-dependent infiltration rate and cumulative infiltration are proposed in this paper. Although the time-range of validity is limited due to the chosen mode of derivation, the formulae seem well suited for application in the course of storm runoff modelling for small catchments. Major advantages of the proposed equations are constituted by the comparatively simple structure and by a high degree of versatility allowing a considerable number of effects to be explicitly accounted for. The parameters involved can be identified from measurements. Rules of thumb regarding the range of applicability are given.