Pulmonary diffusing capacity was measured in eighteen subjects on twenty-one occasions. On fourteen occasions, atropine was administered, and the DL three-quarters of an hour later fell significantly. Seven pairs of observations at intervals of three-quarters of an hour, without the intervening administration of atropine, showed no significant change in DL. It is concluded that the administration of atropine, in the circumstances of these observations, causes a significant fall in DL. It is suggested that this fall cannot be adequately explained on the basis of an increased respiratory deadspace, but is compatible with a shift of blood out of the lungs.