Abstract: In a process for rapidly and inexpensively diagnosing malignant diseases or their precursor stages, samples of arterial and/or capillary blood and of venous blood are withdrawn from a patient and the percentage shares of three groups of blood cells in the blood samples are determined wherein a first group includes blood cells of a size ≦8 &mgr;m, a second group includes blood cells of a 9 &mgr;m and 10 &mgr;m and the third group includes blood cells of a size ≧11 &mgr;m. The percentage shares are multiplied by weighting factors &agr;1 and &bgr;1, and the values y=&Sgr;&agr;i[(Ni)A]−&Sgr;&agr;i[(Ni)V] and x=&Sgr;&bgr;i[(Ni)A]−&Sgr;&bgr;i[(Ni)V], are calculated and from the locations of x and y in an x/y coordinate system, the presence of Ca. corp. uteri or its precursor stages is determined.