Looking at valid results obtained so far, we thought it of interest to apply the MALDI-MS approach to the study of plasma samples from patients with colon or rectum cancers and to compare the peptide patterns so obtained with those from healthy subjects, with the final aim of establishing some peptides useful as markers of the disease. For this preliminary study, plasma samples from nine healthy subjects, 10 patients affected by colon cancer (stage IV) and 11 patients with rectal cancer, randomly chosen, were analyzed. Interestingly, at first sight, clear differences were observed among the MALDI spectra of plasma samples from healthy subjects and colon and rectal cancer patients, as shown by spectra, typical of the three classes of subjects. However, in order to evaluate the real significance of these differences, some data elaborations were performed. Among the large number of peptides not detected in healthy subjects which are present in colon and rectal cancer patients, some of them are common between the two groups of cancer, whereas some others appear to be specific for colon cancer only. It should be emphasized that the species at m/z 1917, detected for both the sample sets in the case of the different spectra of plasma samples from rectal cancer patients shows a mean relative abundance higher than that observed in the case of colon cancer (21 š8 vs 7š 2, respectively). In conclusion, our data suggest that some ionic species detected by MALDI-MS in the plasma of patients affected by colorectal cancer could be of interest for a more complete molecular classification of the disease, and might provide new information for the development of clinical diagnostic and prognostic tools. Of course, these results represent only preliminary data on low molecular mass plasma peptides. They are, in our opinion, promising but further studies on a larger set of plasma samples and using different fractionation procedures are required, and work is in progress along these lines.