The clinical and histological findings in an animal model of ocular cell mediated immune responses are described. These were evoked in sensitised guinea-pigs by dropping tuberculin into the conjunctival sac or injecting it under the palpebral conjunctiva. When tuberculin was dropped into the conjunctival sac, higher doses were required to evoke a strong response than when it was injected subconjunctivally. When high doses of antigen were used for challenge, a mild response was observed in unchallenged contralateral eyes. The cellular response at low doses of tuberculin consisted predominantly of mononuclear cells. At higher doses the cellular infiltrate was more pronounced, and polymorphonuclear cells tended to predominate 24 hours after challenge, while at 48 hours mononuclear cells predominated.