Tissue engineering may be a promising approach for the treatment of focal articular cartilage defects. Programmed cell death (apoptosis) plays an important role in multiple degenerative processes of cartilage (e.g. osteoarthritis). It is known that matrix provides a trophic signal for the cells and an altered matrix may influence the availability of factors that regulate apoptosis. In this study we investigate the viability of chondrocytes seeded on a Chondrogide scaffold (Geistlich Biomaterials, CH), which we use in matrix-induced autologous chondrocyte transplantation (MACT). By now, we have studied material from 29 patients treated for localized articular cartilage defects in the knee. Our results indicate that light microscopy (Mayer's hematoxylin-eosin, Masson-Goldner, Trypan-blue and TUNEL method) and electron microscopy can be used to investigate for apoptotic cells grown on a Chondrogide resorbable scaffold. Neither the handling of the cell-matrix biocomposite nor the procedures for fixation could destroy the scaffold or the cell sheet adhering firmly to the matrix. Apoptotic cells were revealed in all samples and with all techniques used. Mayer's hematoxylin-eosin and Masson-Goldner staining show cells with a condensed, pycnotic nucleus and shrunken cytoplasm. In electron microscopy we observed cells with chromatin condensation and volume shrinkage consistent with apoptosis. The results of the Trypan-blue staining show a mean viability of 92.1 +/- 9.8% (range 57-100%). The TUNEL method revealed 44.6 +/- 20.4% positive cells. Our results indicate that apoptosis plays an important role in chondrocytes grown on a scaffold. An optimal scaffold will determine the growth, morphology and phenotype of the chondrocytes by its physical and chemical characteristics.