Fascioliasis is a zoonotic parasitic disease caused by Fasciola hepatica and F. gigantica. Emergence of human fascioliasis prompted a worldwide control initiative including a pilot study in several countries. Given the necessity to characterize the fasciolid populations involved, the overall aim of the present research is, first, the phenotypic characterization of faciolid adults and eggs implicated in human endemic areas, where this initiative has been implemented, through a computer image analysis system (CIAS) applied on the basis of standardized measurements. Second, new immunological techniques and their potential use as immunological diagnostic tests in those areas are evaluated. The specific results have been grouped into five parts. A) Characterization of eggs of both F. hepatica and F. gigantica for their differential diagnosis. The study revealed that eggs shed by humans show morphological traits different from eggs shed by animals. In humans, F. hepatica eggs are bigger and F. gigantica eggs are smaller than reported to date from livestock, and their measurements overlap when compared. B) Study of the correlation between egg-shedding and uterus development in F. hepatica human and animal isolates. Uterus area (UA) development of adult F. hepatica obtained at different days post infection (dpi) in a Wistar rat model with isolates obtained from cattle, sheep, pigs and humans from the endemic human fascioliasis zone of the Northern Bolivian Altiplano was analysed and compared with the number of eggs shed per gram of faeces as obtained through the Kato–Katz technique. This work shows a positive correlation between liver fluke UA and egg production. C) Study of F. hepatica phenotypic characterization in Andean human endemic areas. The results showed that two phenotypic patterns could be distinguished in F. hepatica adult size: the valley pattern (Cajamarca and Mantaro, Peru) and the altiplanic pattern (northern Altiplano, Bolivia). Furthermore, the Andean valley population and European standard populations presented phenotypic homogeneity. The Altiplano population showed a large size range with a pronouncedly lower minimum size, indicating that uterus gravidity is reached at a smaller size than in valley populations. D) Study of the DRG Fasciola hepatica IgG ELISA test as a serological diagnostic tool of human fascioliasis in different epidemiological situations. The study shows that sensitivity and specificity of the DRG assay were 95.3% (95% confidence intervals, 82,9–99,2%) and 95,7% (95% confidence intervals, 92,3–97,5%), respectively. No correlation between egg output and the optical density (OD) values of the test was observed. E) Field evaluation of the MM3 coproantigen detection test for fascioliasis diagnosis and surveillance in human hyperendemic areas of Andean countries. As part of the above-mentioned control initiative, two hyperendemic areas were chosen: Huacullani, Northern Altiplano, Bolivia, representing the Altiplanic transmission pattern with high prevalences and intensities; the Cajamarca valley, Peru, representing the valley pattern with high prevalences but low intensities. It can be concluded that the coproantigen-detection test allows for high sensitivity and specificity, fast mass screening, detection in the chronic phase, early detection of treatment failure or reinfection in post-treated subjects, and is convenient in surveillance programmes. However, this technique falls short when evaluating the fluke burden on its own.