Abstract: In a method for early diagnosis of human cancer, a human fecal sample of bacteria (Escherichia coli and/or Streptococcus faecalis), is incubated in vitro with a standard culture of a known number of cancer cells, for a period of time sufficient to enable the extent of interaction between the bacteria and the standard culture of cancer cells to be determined; the number of the interacted and/or non-interacted cancer cells present at the end of the period is determined and is utilized for the diagnosis based on the calculation of a tumor cell necrosis index (TCNI). The extent of interaction referred to may be calibrated against analogous interaction using a control preparation of bacteria, e.g. Escherichia coli A.T.C.C. 55373, 55374 and/or 55375, and/or Streptococcus faecalis A.T.C.C. 55376.