Computerized chromosome analyses have resulted in up to 25% erroneous classifications, whereas a cytogenetically trained laboratory technician has an error rate of less than 0.1% in the preparation of a karyotype. In the project reported here, computerized classification is eliminated, and instead, the other steps of the analysis leading to the final karyotype are automated. In the instrument is a projection microscope, modified to project the image on paper before the operator. The slide is scanned on a motor-driven scanning table, in search of a suitable metaphase. The operator stops the scanning motor when a suitable metaphase comes into view. The individual chromosomes of the metaphase are then framed, using a view finder, and are identified, after which the chromosome number is entered on a kayboard. The instrument automatically ensures that, for each data entry, the framed chromosome is photographed in such a manner that the chromosome is placed in the proper location with the correct orientation in the karyotype. When all chromosomes have been identified, and the data have been keyed in, a photograph of the finished karyotype is presented. Marking the metaphase chromosomes on the paper, chromosomes are counted within 20 s. With conventional methods, a total chromosome analysis takes 3-6 h, but the above-described device requires 20-30 min.