At Songklanagarind Hospital, a protocol for chemotherapy in breast cancer has been used since 1994. The purpose of this study was to examine "non-medical" factors that may reflect non-acceptance of this protocol. A retrospective review of charts of 160 consecutive patients with breast cancer from July 1996 till June 1997 was made. The approved protocol (P) was cyclophosphamide, methotrexate, fluorouracil (CMF). The majority (78.8%) of the total 160 patients or 93.3% of those given antineoplastic drug were prescribed the approved protocol. Nonprotocol (NP) drugs included epirubicin, paclitaxel, etoposide and cisplatin. Decisions to change to non-protocol treatment appeared to be dictated by the type of payment and the stage of disease. Cost of nonprotocol chemotherapy was 15 times higher per person or 20 times higher per visit. It is suggested, from this review, that protocol evaluation should be done continuously by participants that may lead to an optimum protocol.