An experimental investigation of the effect of exposure to biological fluids on the adhesion of silicon modified DLC films to steel substrates (304 stainless and mild steel) was conducted. The substrate straining test was used for the adhesion measurement. A statistical procedure, which is faster and more reliable than the ab initio computer simulation of crack spacing distribution adopted by previous authors in the literature was used to treat the crack spacing data. We observed a change in the crack spacing distribution from the Weibull for the as-prepared films to Lognormal for the films immersed in biological fluids. A reduction in the interfacial adhesion values was also observed for the films soaked in biological fluids compared to the as-prepared films. The proposed approach can be used when the crack spacing matches other statistical distributions. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.