To date, largely because of convenience, therapeutic trials in progressive systemic sclerosis have been few and largely short-term retrospective single institution studies. For the future, there is a pressing need to expand efforts in this area to include: controlled, prospective studies with adequate numbers of patients employing, if necessary, a multicentre effort; careful classification of PSS patients into meaningful disease subsets and inclusion of this concept into experimental design; development and testing of criteria for disease staging and severity; refinement of current objective criteria for change (improvement or deterioration) and development of new, simple-to-perform, quantifiable descriptors for skin and internal organ involvement which are properly validated; studies of adequately long duration to avoid failing to detect significant differences between cases and controls; and attention to disease duration in study design, with special emphasis on choosing patients with early disease. A great deal of clinical epidemiological research will be required for progress in patient classification and improvement of methods of patient assessment. Careful planning of therapeutic trials and the inclusion of biostatistical expertise in the design phase of such studies is desirable if we are satisfactorily to answer the questions posed by each trial.