Production in Spanish biomedical main-stream science in the years 1986-1989 was studied. A series of bibliometric and socioeconomic indicators were applied to determine the geographical distribution, the institutions involved and the most active centres per speciality using their scientific output, their impact and their basic-clinical type of research. A great heterogeneity was observed between the autonomous communities, with Madrid and Cataluna being in an outstanding position. This bifocal centralization is stronger when the main-stream research output of hospitals is considered in contrast to the more homogenous distribution of hospital care. The consequences of these observations are discussed. The average level of the Spanish research output is basic; clinical papers are mostly published in national journals which are scarcely covered by the database used. This might be the reason for the non-correlation observed between research output per speciality and causes of mortality and morbidity. The indicators for each particular centre are compared with those of the whole of Spain for each speciality in order to find 'centres of excellence'. The results of Spanish research are published in journals of a similar impact to those used by other European Union countries, although the number of citations received is much smaller, as has already been observed for other disciplines in Spain and peripheral countries.