Abstract: Oxalysine (Ⅰ-677) was found to be a new antitumor antibiotic which was isolated from the culture media of Streptomyces roseoviridofuscus, n. sp. obtained from the soil in Dalien region, China by the Department-of Antibiotics of this Institute. In this paper its therapeutic action on murine brain tumor-22 (B-22) was studied with different routes of administration and different schedules of treatment. When the drug was injected either intravenously, intraperitoneally, intragastrically or intramuscularly at total dosages of 1～1.5 g/kg a marked therapeutic effect was observed, the tumor inhibition rate being about 47～78%.In dogs intravenous injections of oxalysine 200～400 mg/kg caused no significant changes in blood picture, EKG, liver and kidney functions. No toxic reaction was observed when a monkey was given 100 mg/kg.The absorption, distribution and excretion of ³H-oxalysine in mice were also investigated. Following a single intravenous or intragastric injection of 200 mg/kg of ³H-oxalysine, the ³H content was found to be highest in the liver. The radioactivity in the tumor was not high, but persisted for more than 48 hours. The radioactivity was excreted mostly in the urine, about 63% of given dose could be detected within 24 hours.