Aims Preliminary results indicate higher absorption of tricalbendazole (TCBZ) administered postprandially. Therefore, the influence of food on the pharmacokinetics of TCBZ and its active sulphoxide (TCBZ-SO) and sulphone (TCBZ-SO2) metabolites was investigated. Methods Two single doses (10 mg kg-1) of TCBZ were administered to 20 patients with fascioliasis. Ten patients were first given the drug after a high energy breakfast and then, 48 h later, after an overnight fast. The others 10 patients first received the drug in fasting state and then, 48 h later, after breakfast. A low energy breakfast was served 2 h after drug administration for fasting state. Results Compared with the fasting state, an increased AUC and C(max) after food intake (significant, P<0.0001) was shown from the values of TCBZ, TCBZ-SO and TCBZ- SO2. The mean AUC for TCBZ (fasting: 1.55, fed: 5.72 μmol l-1 h), TCBZ-SO (fasting: 177, fed: 386 μmol l-1) and TCBZ-SO2 (fasting: 13.9, fed: 30.5 μmol l-1 h) indicated a large availability increase with food and the strong systematic predominance of the active sulphoxide metabolite over the required a second course of two postprandial doses of tricalbendazole (10 mg kg-1 each). Tolerability to the treatment among the patients was good. Conclusions: The administration of triclabendazole with food is recommended for improved systematic availability in patients with fascioliasis or paragonimaiasis.