Apart from the hydrolysis of acetylcholine (ACh), acetyl- (AChE) and butyrylcholinesterase (BChE), through noncatalytic mechanisms, intervene in hematopoiesis, morphogenesis, and neurogenesis (Layer and Willbold, 1995; Soreq and Seidman, 2001). Cholinesterase (ChE) molecules occur as globular (G1, G2, and G4) and asymmetric (A4, A8, and A12) forms (Legay, 2000; Massoulié, 2002). The G species might display amphiphilic (GA) or hydrophilic (GH) properties (Perrier et al., 2002). The involvement of ChEs in tumorigenesis is supported by the measurement of ChE activity in tumors (García-Ayllón et al., 2001; Ruiz-Espejo et al., 2003), the amplification of ChE genes in leukemias and ovarian tumors, and the relationship between the expression of AChE and the aggressiveness of astrocytomas(Perry et al., 2002). This research was undertaken to determine whether ChE activity is altered in gut carcinomas.