In situ end-labeling (ISEL) of internucleosomal 3' DNA strand breaks and the morphological proof of nuclear chromatin condensation are two widely used methods to investigate and quantify apoptosis. However, it is still unclear whether both processes are linked with each other and if quantifying apoptosis by both methods leads to comparable results. Therefore, internucleosomal DNA fragmentation and chromatin condensation were measured simultaneously on double-fluorescence-labeled sections of 62 testicular tumors (47 nonseminomatous tumors and 15 seminomas) using immunofluorescence microscopy. Different apoptotic indices (AI), based on DNA fragmentation and/or morphological criteria were determined. The AI were quantified. Morphologically obtained AI ranged between 1.99% for non-seminomatous tumors and 0.88% for seminomas. The detection of DNA fragmentation values ranged between 8.15% for non-seminomatous tumors and 2.70% for seminomas. Only about 30% of all apoptotic cells could be detected with the morphological method compared to 80% using ISEL in both tumor entities. Therefore, the equivalence of investigations using different apoptosis detection methods in human testicular cancer seems questionable.