The insertion of a catheter into the inferior vena cava for venoclysis is sometimes a lifesaving measure, but it carries a significant degree of risk. In most of the 24 cases here studied the catheter was inserted through a needle into a femoral vein and threaded into the vena cava. Thirteen patients tolerated the indwelling catheter for from 3 to 14 days with no complications. The remaining 11 patients suffered various complications. Four cases are presented in some detail to illustrate the four principal complications encountered: local thrombosis, thrombosis with embolism, suppurative thrombophlebitis with septicemia, and chemical necrosis resulting from the infusion of irritant solutions. The results were fatal in three of these cases. Among the most important contraindications are thrombophlebitis in the lower extremity, infection about the site of insertion of the catheter, and pelvic inflammatory disease. If the use of a caval catheter is indicated, rigid asepsis must be maintained, infusion of solutions known to be irritant or sclerosing action should be avoided, and the flow should be slow and constant rather than intermittent. The caval catheter is a valuable therapeutic tool, but it must be used with due regard to limitations and hazards.