Marimastat (BB-2516) is the first orally bioavailable matrix metalloproteinase inhibitor to have entered clinical trials in the field of oncology. It has excellent bioavailability and has completed Phase I, II and some Phase III trials. In Phase I studies, which recruited patients with various malignancies, the main toxicity observed was mild to severe joint and muscle pain seen in > 60% of patients receiving a dose of marimastat > 50 mg b.i.d. The symptoms were reversible on discontinuation of the drug and their incidence has been reduced by using marimastat 10 mg b.i.d. In a number of Phase II studies in a variety of tumours, serum tumour markers were used as surrogate determinants of efficacy. Results were interpreted as indicating activity, but this has not yet translated into improved survival in the Phase III studies, which have been completed in pancreatic or gastric carcinoma and glioma. It is likely that these drugs will be most effective in the setting of minimal tumour volume such as in adjuvant treatment or maintenance therapy following response to standard cytotoxics. Therefore, the analysis of Phase III studies in small cell lung cancer (SCLC) where this hypothesis has been tested is awaited with interest. Marimastat can be safely co-administered with conventional cytotoxics and radiotherapy and Phase III studies using these approaches are currently ongoing.