Methotrexate sodium, cytarabine and hydrocortisone sodium succinate were evaluated in three vehicles, Sodium Chloride Injection, USP, Lactated Ringer's Injection, USP, and Elliott's B solution, an artificial cerebrospinal fluid (CSF). Osmolarity values of all drug solutions studied were within 10% of normal human. No vehicle-related alterations in the stability of methotrexate or cytarabine were detected under simulated use conditions. However, the degradation of hydrocortisone sodium succinate was faster in Elliott's B solution than in the other vehicles. Principal differences among the vehicles involved electrolyte content, pH and buffer capacity. Elliott's B solution is similar to CSF in electrolyte composition and buffer capacity, and was the only vehicle to maintain the pH of dilute methotrexate and cytarabine solutions between 7.2 and 7.8. The significance of these in vitro data await a careful clinical study.