The effects of microscope slides coated with Poly-L-Lysine (PLL) on the heterogeneous nucleation of tetragonal hen egg-white lysozyme (E.C. 3.2.1.17, HEWL) have been investigated using batch method. It was found that the PLL coated glass substrate selectively controlled the orientation of tetragonal lysozyme crystals to either {111} or { 101} form depending on supersaturation. The effects of molecular weight (MW) of PLL coatings on the orientation of crystals were examined. The higher MW of PLL, the higher ratio of {110} crystals was observed. The total number of crystals retained on the coated glass substrate decreased by 20% compared to the normal glass. Furthermore, the effects of the concentration both of HEWL and NaCl on the morphology were also examined. It appears that the ratio of longer axis/shorter axis (as shown in the Fig. 2) tended to approach 1, when the supersaturation was increased in 1.6 < σ < 3.2. (C) 2002 Elsevier Science B.V. All rights reserved.