In cytological investigations to trace gynecological cancer a large number of preparations must be examined in order to discover a small number of positive and suspicious findings. In 1974, 5.5 million investigations were carried out in the German Federal Republic, of which 2% positive, 9.2% suspicious and 2.4% technically useless cytological results were obtained. 98.64% of the cytological results were negative. Consequently in different parts of the world efforts are being made to automate the preliminary microscopic sampling of the cytological preparations. False negative cytological findings must be no higher than in conventional diagnosis (without extraction error approximately 5%), while false positive cytological findings (in conventional diagnosis less than 1%) may be higher, because they can be classified correctly on subsequent assessment.