Biogenic erosion processes acting on present day limestone coasts in the Northern Adriatic were observed over a period of 2 yr. High precision determinations of the rates of these processes were obtained by in situ measurements. A mathematical model derived from the measurements was used to extrapolate recent erosion rates over a range of time of .apprx. 1000 yr. The coastal profiles suggested by the modeling underline the primary importance of biological erosion for the morphology of limestone coasts. Size and shape of granular erosion products are largely controlled by the boring habits of endolithic microorganisms [Cyanophyta, Patella coerulea, Monodonta turbinata, Littorina neritoides and Paracentrotus lividus]. The distribution of these erosional products and their contribution to sediment production were studied by sedimentological analyses of nearshore sediments.