Neurologic deficits have followed the intrathecal injection of 2-chloroprocaine 3% (10(-1) M) with sodium metabisulfite 0.2% (10(-2) M) as a preservative. This study evaluated the effects of varying concentrations of 2-chloroprocaine and sodium metabisulfite, as well as the combination of the two, on the vascular reactivity of isolated rings of rat thoracic aorta. Isolated Sprague-Dawley rat thoracic aortic rings were prepared and connected to force transducers for measurement of isometric tension. The tension produced by log-arithmically increasing concentrations of 2-chloroprocaine, sodium metabisulfite, and their paired combination was measured. Sodium metabisulfite concentrations below 0.2% (10(-2) M) caused a maximum of 40% vasoconstriction compared to control followed by vasodilation with a maximum of 80% at 10(-2) M (the concentration in the former clinical preparation). 2-chloroprocaine alone produced a progressive relaxation at 10(-3) M or higher concentration with a maximum of 130%. The effects of the mixture of sodium metabisulfite and 2-chloroprocaine were identical to the effects produced by 2-chloroprocaine alone. The relaxation effects of 2-chloroprocaine dominate the vasoconstricting effects of sodium metabisulfite when the two drugs are combined.