Results of investigation about Enterovirus-70 (EV-70) as an etiologic agent of epidemic of acute haemorrhagic conjunctivitis (AHC) and neurological disease in the metropolitan area of São Paulo city are presented. During the first three months of 1984, in an epidemic period of AHC, 3 groups with a total of 291 persons were studied. The group A included 90 individuals affected by AHC; the 99 persons belonging to group B did not acquire the AHC but refered familiar contact with the ill individuals; the group C included 102 persons who denied the AHC or any contact with the illness. Neutralization test in BHK-21 cell culture was used for measurement of antibodies in sera. For the detection of the presence of IgM, indirect immunofluorescence assay was utilized. The presence of IgM antibodies was observed in 56.7%, 33.3% and 20.6% of persons belonging to groups A, B and C, respectively. The 10-29 age group was the most affected in the group A. From april 1984, after the end of epidemic period of AHC, until December 1987, three sporadic cases of AHC and 10 cases with acute neurological disease associated with recent infection by EV-70 were observed. Nine of 10 persons with acute neurological symptoms had paralysis of cranial nerves, all of them recovering without sequelae. The circulation of EV-70 in the population during the endemic period was maintained by either asymptomatic, sporadic cases of AHC or neurological diseases.