Objective       To screen the differentially expressed proteins and peptides in the serum of patients with colorectal cancer (CRC) using two-dimensional electrophoresis mass spectrometry (2DE-MS).       Methods       Serum samples were obtained from 15 CRC patients (CRC group) before operation and 10 healthy volunteers (control group)

and then pretreated for removing albumins and immunoglobulins and desalting. The differentially expressed protein spots were observed by comparing 2DE-PAGE gel maps between the CRC group and control group

and were identified by MALDI-TOF mass spectrometry.       Results       Compared with that of the serum samples without pretreatment

the volume of the pretreated serum samples increased

and more protein spots were detected. The comparison of the 2DE-PAGE gel maps between the CRC group and control group showed two differentially expressed protein spots

which were identified as transthyretin (TTR) and cytokeratin-1 (CK-1) by MS. TTR was lowly expressed and CK-1 was highly expressed in the serum of the CRC group. The serum level of TTR in the CRC group (245.87±60.72 mg/L) was significantly lower than that in the colorectal adenoma group (299.53±67.91 mg/L) and control group (311.31±67.01 mg/L) (P0.01).       Conclusion       2DE-MS is a useful tool for screening and identifying disease serum markers. TTR may be a potential serum marker of CRC.