Pentoxifylline improves microvascular blood flow in conditions of vascular insufficiency. The clinical benefits of pentoxifylline have been attributed to its effects on the cellular elements of whole blood, although a few studies suggest it may also be a vasodilator. The purpose of this study was to determine whether pentoxifylline has a vasodilator effect on the luminal diameter of small arteries preconstricted with norepinephrine and on resting small arteries in the rat cremaster muscle. Intravital videomicroscopy was used in order to observe directly the vasodilator capacity of topically applied pentoxifylline. The results reveal that pentoxifylline (100 microM and more) can significantly dilate small arteries preconstricted with norepinephrine. Pentoxifylline had no effect on the diameter of resting small arteries. These results suggest that vasodilation may play a role in the ability of pentoxifylline to improve arterial blood flow.