Adult worms develop in dogs and their eggs are shed in the feces. Non-embryonated eggs of Toxocara canis become infectious after about 2-6 weeks in the soil and the likelihood of their transmission to humans is through ingestion. In 2004 studies were carried out in the areas of urban recreation in the central region of Argentina. A total of 393 dog excrement samples were collected in eight different cities: 59.3 per cent were positive for parasites. These areas of urban recreation are contaminated with zoonotic parasites in the cities of Paraná (19 of 24 areas), Santa Fe (20 of 26), and Santo Tomé (14 of 18). Eggs of T. canis were present in 101 of 393 (25.7%) of the excrement samples, and eggs could be found in 53 of the 68 (77.9%) areas of urban recreation studied in these cities. This contamination is greater in areas of lower socio-economic conditions. The object of this paper is to discuss markers of parasitic contamination with the aim of triggering the necessary control measures.