Pigeons were subjected to changes in G-loading during parabolic flight with special attention to their flight behaviour in the weightless periods. Experiments were performed 1) with the eyes covered, 2) with the legs tied to the body, 3) with eyes covered and legs tied, and 4) with none of these handicaps. In all these situations the flight behaviour of the birds was observed. Special attention was paid to the tumble-phenomenon, which appeared birds with covered eyes. The results are discussed and comparisons are made with the behaviour of man and fish under similar conditions.