The 1,4-β-D-glucan cellobiohydrolase I (CBHI) from Trichoderma reesei was labelled with 4–6 nm gold particles. This CBHI-gold complex still retains 60% of the original CBHI activity and allows good visualization of the enzyme adsorbed at the surface of cellulose mirofibrils or microcrystals. The main features of the adsorption are: rapid and irreversible binding; preference of the crystal edges instead of the crystal surface for the binding; the absence of specificity for the crystal tips where the cellulose chain ends are supposedly located.