It is a live virus vaccine containing a carefully selected fowl Laryngotracheitis virus strain modified by passage in tissue culture. Because of the highly modified character of this vaccine, it does not offer the same degree of protection usually obtained from more virulent products. This vaccine contains a very mild attenuated virus and there is no danger of seeding down the premises with Laryngotracheitis virus which can spread and cause the disease. It is used for chickens 4 weeks of age or older as an aid in preventing fowl Laryngotracheitis through immunization by the Eye Drop Method. The vaccination should be repeated from the age of 10 weeks.