Nucleotidase cascades (apyrase, 5' nucleotidase, and adenosine deaminase (ADA) were investigated in the parasitic trematode Fasciola gigantica. ADA had the highest activity in the nucleotidase cascades. Adenosine deaminase was purified from F. gigantica through acetone precipitation and chromatography on CM-cellulose. Two forms of enzyme (ADAI, ADAII) were separated. ADAII was purified to homogeneity after chromatography on Sephacryl S-200. The molecular mass was 29 KDa for the native and denatured enzyme using gel filtration and SDS-PAGE, respectively. The enzyme (ADAII) had a pH optimum at 7.5 and a K(m) 1.0 mM adenosine, a temperature optimum at 40 degrees C and heat stability up to 40 degrees C. The order of effectiveness of metals as inhibitors was found to be Hg(2+)>Mn(2+)>Cu(2+)>Ca(2+)>Zn(2+)>Ni(2+)>Ba(2+).