Seventy-one frozen lung tissue specimens from 52 patients suffering from non-small cell lung cancer (NSCLC) were analysed in this study. Cryostat sections were stained with monoclonal antibodies against p53, ki-67 and p120, all of which are of prognostic value in NSCLC. Slides were evaluated by standard manual microscopy (MM) and using a new Automated Cellular Imaging System (ACIS). The results obtained with ACIS correlated significantly with MM examination (p<0.001). However, ACIS showed a higher sensitivity, especially for specimens with a low infiltration volume. In 15 (6.8%) MM negative cases singular positive cells were identified with ACIS. In cases with a high infiltration volume subjective (MM) quantitation tended to overestimate the number of infiltrating cells. ACIS guaranteed a high reproducibility of data. We conclude that ACIS-assisted analysis is a valid means of investigating the p53, ki-67 and p120 antibody expression in cryostat sections of lung cancer specimens. ACIS can complement conventional manual microscopy due to its higher accuracy, sensitivity and better reproducibility of data.