Passive transfer experiments were carried out on three species of monkey, Macaca mulatta, Macaca nemestrina and Macaca fascicularis, using human serum from patients affected with severe symptomatic dermographism (factitious urticaria), cholinergic urticaria, chronic idiopathic urticaria and normal subjects. The monkeys were tested for dermographism by means of a calibrated dermographometer 24 h after intradermal injection of the serum, using Evans blue as a marker. Positive responses were seen initially in the M. nemestrina. Four sites injected with serum from patients with severe symptomatic dermographism gave positive responses, one site injected with serum from a normal subject produced a faint response. One of the four responses was reproduced one month later in M. fascicularis. These results indicate that passive transfer of dermographism is possible from human to monkey.