The study investigated the prevalence, risk factors, and nutritional consequences of intestinal parasitic infections (IPI) in rural Ecuadorian children. A total of 244 children aged 0.2-14 years were studied. The data were collected using a structured questionnaire, anthropometry, and laboratory analysis of blood and fecal samples. The results showed that 90 per cent of the subjects were infected with at least one pathogenic IPI: 51 per cent with helminths, 37.6 per cent with protozoa, and 21.4 per cent with both. Giardia-infected children had a risk for stunted growth that was twice that of other children (51.7 vs. 33.1 per cent; OR = 2.16, 95 per cent CI = 1.13-4.15; p = 0.01). They also had significantly reduced mean hemoglobin levels compared with their non-infected counterparts (11.8 +/- 1.5 vs. 12.2 +/- 1.4 g/dl; p = 0.023). However, the proportion diagnosed with iron-deficiency anemia was slightly, but not significantly, increased (29.4 vs. 24.3 per cent). The most consistent predictor of Giardia and other protozoal IPI risk was a high intra-/peri-domicilliary concentration of domestic animals. Children who lived in such households had an infection risk that was two to five times greater than that of their non-infected counterparts. The data indicate that Giardia intestinalis infection has an adverse impact on child linear growth and hemoglobin. They also suggest that domestic animals may be an important reservoir for Giardia and other intestinal protozoal infections observed in the Ecuadorian children studied.