A detailed examination of the possible sub-divisions of autogenic percolation cave inflows, employing data from G.B. Cave, Mendip Hills, generally supports previous classifications. Two major groups comprising quickflow and baseflow can be further sib-divided into four classes which correspond with the general morphological descriptions: subcutaneous flow, shaft and vadose flow, percolation streams and seepage flow. The most important properties of percolation flow behaviour are maximum discharge, reflecting fissure transmission capacity, and discharge variability, reflecting available storage. Classifications based on carbonate hardness are considered of limited use due to the possible evolution of percolating water with depth and to differences in the nature of recharge area. However, the variability of carbonate hardness is related closely to variability in discharge and functions equally well as a discriminatory variable.