In this study, a scanning microscopic computer-assisted image analysis system was used for the immunocytochemical characterisation of collagen types I, III and V in normal human fibroblasts from pulp and gingival explants, using specific purified antibodies and peroxidase labeling. The culture conditions were standardized in order to evaluate simultaneously the expression of the three antigens in four different culture passages of the two fibroblast types. The optical density values of immunostaining intensities were quantified, the integrated optical density per cell was calculated, and the results were analyzed by a variance test. It was found that all three collagen types were present in the tissues, and in both gingival and pulp fibroblasts after three to nine culture passages. A non-parametric statistical analysis of the staining intensity variances revealed significant differences between antigenic levels depending on the tissue origin of the fibroblasts and an effect of culture passages. The results seemed to justify application of this technique at the light microscope level for the evaluation of collagen production, the principal function of fibroblasts, but the tissue origin and number of culture passages should be taken into consideration for in vitro biocompatibility testing of dental materials.