Differences in pain intensity, surface area measurements of induration and erythema, and interstitial fluid volume when warm versus cold applications were randomly made to an intentional intravenous infiltrate of 5 mL of a designated solution were examined. Three solutions were used: 0.5 saline (154 mOsm), normal saline (308 mOsm), and 3% saline (1027 mOsm). Differences in volume were determined by magnetic resonance imaging (MRI) at three intervals postinfiltration. The sample was 18 healthy adults between 20 and 45 years. There was no difference in remaining infiltrate when 0.5 saline or normal saline were used, but a significant (p < 0.001) difference was found with 3% saline. For all solutions there was a significant (p < 0.001) difference in the volume of infiltrate remaining when warmth was applied and this effect held across MRI readings and solutions. Pain intensity did not differ by treatment but a significant (p < 0.005) difference was found by solution, with 3% saline producing the greatest difference. Erythema was absent with all solutions. Surface induration was affected by solution and decreased over time (p = 0.001). There was no effect of warmth or cold on surface area induration. © 1993 John Wiley & Sons, Inc.