1. Gravity-fed intravenous infusions were studied in patients by using continuous flow recording and a new resistance-measuring method.
2. A common, though preventable, cause of reduced flow was the gradual deformation of the plastic tubing under the regulator clamp.
3. In many cases there was some constriction of the cannulated vein and in a few this constriction was severe enough to seriously impair the infusion. The severity of the constriction varied periodically.
4. There was no evidence of trouble due to a generally raised pressure in the arm veins nor was clotting in the cannula a serious problem.
5. A simple test is described which may be found useful clinically for assessing the difficult infusion.