General toxicity (A) and vein damaging properties (B) of 5-hydroxymethyl-2-furfural (HMF) were studied in rabbits. A. 400 mg HMF was given as subcutaneous injections twice a day for a week. It was not possible to demonstrate any harmful effect of the injections on the following parameters: weight, haemoglobin, leucocytes, platelets, serum-protein, serum-alanine-aminotransferase, alkaline phosphatase, liver cell necrosis or hepatic steatosis as compared with a control group. B. Addition of 200 mg HMF/l isotonic NaCl solution did not increase the vein irritating effect of the solution, when given as a 5 hours' continuous intravenous infusion. The amounts of HMF used in this study far exceeded what patients receive from glucose solutions.