A randomized, double blind comparison of the incidence of removal of patches because of venous occlusion was performed in patients on continuous intravenous fluid therapy using 2.5 mg trinitroglycerine or placebo patches attached to the thorax. The sample comprised 90 patients, of whom nine were excluded for administrative reasons. Of the remaining 81,41 received active and 40 received placebo patches. Within one week 11 venflones occluded; ten in patients on placebo, and one in a patient with an active trinitroglycerine patch. Finally 14 (11 placebo and three trinitroglycerine) patches occluded. This tendency in favour of trinitroglycerine patches was statistically significant (p = 0.018). No difference in frequency of thrombophlebitis was observed: (14 versus 18 not leading to occlusion). Seven patients on trinitroglycerine and one on placebo developed moderate headache which did not necessitate withdrawal of treatment. It is concluded that 2.5 mg trinitroglycerine patches seem to improve survival of venflones used for continuous, intravenous fluid therapy, even when applied to the thorax.