DISEASE CHARACTERISTICS: Histologically or cytologically confirmed non-small cell lung cancer Stage IIIA/B disease No malignant pleural effusions Minimal residual disease after one or a combination of the following: Incomplete surgical resection i.e., macroscopic residual disease at completion of surgery Radical radiotherapy with no evidence of disease progression at entry Documented complete or partial tumor response following at least 2 courses of cytotoxic chemotherapy No evidence of disease progression during or following prior therapy

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Hematopoietic: Absolute neutrophil count greater than 500/mm3 Platelet count greater than 50,000/mm3 Hepatic: Bilirubin less than 2.0 times upper limit of normal (ULN) AST/ALT no greater than 3.0 times ULN Renal: Creatinine no greater than 1.5 times ULN Other: No acute illness within 1 week of start of study No other illness that would significantly interfere with study outcome No major medical illness that precludes prolonged marimastat administration No second malignancy within 5 years except: Adequately treated basal cell carcinoma of the skin In situ carcinoma of the cervix Not pregnant or nursing Medically approved method of contraception required of fertile women Willing and able to tolerate and comply with study requirements

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: See Disease Characteristics No prior marimastat, batimastat, bleomycin, or busulphan No more than 1 cytotoxic chemotherapy regimen for non-small cell lung cancer Endocrine therapy: Not specified Radiotherapy: See Disease Characteristics Surgery: See Disease Characteristics Other: At least 4 weeks since any investigational drug therapies