Nickel-2,3,7,8,12,13,17,18-octaacetic acid-5,10,15,20-tetra-[3-carboranyl-methoxyphenyl]-porphyrin octamethylester (NiTCP) was given in a Cremophor EL, a polyethoxylated castor oil, and propylene glycol emulsion to BALB/c mice bearing transplanted s.c. KHJJ mammary carcinomas. A total dose of 244 microg NiTCP/gram body weight (gbw) (54 microg B/gbw) was given in 6 i.p. injections over a 32 hr period. Observations of behavior and changes in body weight and chemical and hematological blood tests indicated little or no toxicity from NiTCP over a period of 6-90 hr after injections. Boron concentrations near tumor margins were 160-180 microg B/g at 41-90 hr after the last injection. Tumor:normal brain boron concentration ratios reached approx. 10:1 and tumor:blood ratios reached approx. 250:1 after 4 days. There was no evidence of thrombocytopenia or other potentially important toxicities. Our findings place NiTCP among the leading candidates for pre-clinical experiments aimed toward improvement upon the compounds being tested for boron neutron-capture therapy of glioblastoma multiforme.