We studied 44 patients with type 1 Gaucher's disease (16 non-treated patients and 28 treated with enzyme replacement therapy). We measured serum levels of chitotriosidase (ChT), neopterin, angiotensin-converting enzyme (ACE), adenosine deaminase (ADA) and β-hexosaminidase (Hex) and its major isoenzymes Hex A and Hex B. In the untreated group of patients, the increase in serum levels was ChT>neopterin>ACE>ADA>Hex, with all decreasing significantly in treated patients (p<0.001). Highly significant correlations were obtained between the markers of monocyte/macrophage activation which were tested (p<0.001). However, partial correlations between serum Hex B (with Hex A constant) and ChT, ACE, neopterin and ADA did not reach statistical significance. This suggests that hepatocytes are the major cellular source of this isoenzyme. Similarly, partial correlation of ChT with neopterin, with the other variables constant, was not significant, which would suggest a different expression of these two markers in Gaucher's disease.