The purpose of this study is to evaluate in a rat model if the early removal of an experimental intracerebral mass mimicking an extensive subcortical hematoma improves neurological outcome. Fifty six male Wistar rats were studied. A balloon was placed sterotactically at the level of the striatum. The balloon was inflated to 100 microl for periods of 10, 60 or 120 min (with 10 animals in each group). In 10 animals the balloon was not deflated and there were four sham operated cases. Neurological deficit was evaluated by a blinded observer by means of a clinical scale from 0 to 8 points at 24 and 72 h after inflation. Three additional animals at each inflation period were sacrificed after 6 h for pathological study with hematoxylin-eosin staining. Death rate was 9/10 animals who had permanent inflation, 4/10 in those with 2 h inflation, 2/10 for 1 h inflation and 0/10 for 10 min inflation (P<0.01 in chi square test). Many animals developed a particular clinical syndrome not previously described. Mean 72 h clinical scores (0-8 points) were 7.6 (S.D. 1. 2) for the permanent inflation group, 4.4 (S.D. 3.2) for 2 h of inflation, 2.3 (S.D. 3.2) for 1 h and 0.4 (0.9) for 10 min of inflation (P<0.01 in Kruskal Wallis test). In the pathological study the rate of damaged neurons was significantly higher in the permanent than in transient inflation groups. In conclusion, in this balloon model evacuation of an extensive acute expanding subcortical (hematoma-like) mass must be performed within a limited time window to prevent the development of irreversible neurological deficits or death.