PURPOSE: To obtain the medicine composition containing an octane derivative and exhibiting a microtubule collection-promoting action, a cell multiplication- inhibiting action, an antitumor action, etc.

CONSTITUTION: A microtubule collection-promoting agent contains a 3,7-dioxa-1- azabicyclo[3,3,0]octane derivative of the formula (A, B are a five or six- membered homogeneous or heterogeneous ring; X is O, S; R is OH, a group capable of being converted into the OH in the body) or its salt. In addition, conventional components are suitably compounded and subsequently prepared into parenteral preparations, suppositories or oral administration preparations. The microtubule collection-promoting medicine is administered at a daily dose of 1-40mg, preferably 2-30mg, as the compound of the formula or its salt for an adult (body weight: 50kg) once to three times a day. The medicine is further administered at a daily dose of 0.5-50mg/kg/d as an injection. The compound of the formula has an excellent action enabling to be used instead of taxol, and further exhibits low toxicity and a tumor-metastasis-inhibiting action or an antitumor action also effective for carcinoma obtained multiple resistance.