Clinical studies were carried out on two groups of patients with acute haemorrhagic conjunctivitis (AHC) during an epidemic in 1985 in Northern Nigeria. Group 1 consisted of 99 students attending a girls' boarding school, group 2 of 200 patients selected randomly from 1000 examined at the local clinic. Moderate to severe hyperaemia and papillary responses were present in the palpebral conjunctiva of all patients, and 234 (66%) had subconjunctival haemorrhages. Transient superficial punctate keratitis was noted in over 60% of patients. A transient flare suggestive of a low grade iritis was seen in five patients. No neurological disorders were noted. Serological studies were carried out on patients from group 2. Fifteen paired and 20 single serum samples were titrated against adenovirus type 4 (Ad-4) and enterovirus type 70 (EV-70). Two pairs of sera showed a 4-fold rise in antibody levels to EV-70, whereas the antibody titres to EV-70 in the rest of the sera ranged from 1:20 (no antibody) to 1:160. None of the paired serum samples showed a 4-fold rise in antibody levels to adenovirus. The results of clinical studies and serological findings support EV-70 as a probable cause of AHC in Nigeria.