During a treatment that lasted approximately 100 days beginning at fledging time, four groups of pigeons were kept for ten 3-day periods in an aviary of wire-netting located in Arnino. Here they could acquire a visual experience of the landmarks and leave for exercise flights. During these 3-day sojourns, the birds wore masks which prevented or limited their breathing through the nostrils. For the remaining time the pigeons were unmasked and closed in four cages outdoors that prevented them from seeing the country-side. The cages were of two types, ones with walls of horizontal strips that allowed the flow of air (pervious cages) and ones with vertical walls impervious to air currents (impervious cages). The four groups were kept under different conditions: 1) RP-birds were kept in a pervious cage in Arnino; 2) RI-birds, in an impervious cage in Arnino; 3) CP-birds, in a pervious cage in Miemo, 42 km SW of Arnino; 4) CI-birds, in an impervious cage in Miemo. The results of the test releases, carried out in a location 24.5 km SW of Arnino and 17.8 km NE of Miemo were the following: