Recent studies suggest that continuous infusions of H2-receptor antagonists may be more effective than intermittent iv therapy to control gastric pH for the prevention of stress ulcers. Infusions of cimetidine, ranitidine, and famotidine have been shown either to have a beneficial clinical effect, to control gastric acid secretion, to maintain gastric pH greater than 4, or to have pharmacokinetic properties similar to intermittent doses. In addition, some evidence suggests that continuous infusions may permit the use of lower doses, leading to cost savings. However, as yet there have been no trials that directly compare continuous and intermittent regimens and show improved outcomes with a continuous regimen. Since candidates for parenteral administration of H2-receptor antagonists are most common in the ICU, several practical issues must be addressed. Patients who receive total parenteral nutrition (TPN) may be suitable candidates for continuous infusions of H2-blockers since these agents can be given in the same container as TPN solutions. These patients also usually have a parenteral access site and infusion pump dedicated to TPN administration. In other patients, drug incompatibilities, limited iv access lines, or a lack of infusion pumps may require frequent interruptions of the infusion in order to administer additional medications, which may lead to a loss of gastric pH control. In most patients, administration of an H2-blocker regimen which maintains consistent pH control after intermittent administration may be the most practical method by which to administer these agents.