Oesophageally fistulated (OF) sheep and cattle were used to collect samples from 7 green herbages used in digestibility trials. These samples were treated and dried in different ways. In the case of sheep the treatment of OF-collected samples (total extrusa vs. solid fraction) had a significant effect (P ≤ 0,05) on nitrogen content in only 2 of the 7 forages. With cattle, treatment of sample did not influence nitrogen content significantly (P ≤ 0,05). However, a consistently higher nitrogen content was found in the total extrusa. A highly significant (P ≤ 0,01) positive relationship between nitrogen content in total extusa and the solid fraction of OF-collected samples was found. Drying of total extrusa at a temperature of 50 oC had a significant (P ≤ 0,05) depressing effect on in vitro digestibility. Regression equations describing the relationship between in vitro digestibility of OF-collected samples and in vivo digestibility were derived. Irrespective of sample treatment or drying procedure, a close relationship between in vitro and in vivo digestibility, was found. Different equations for sheep and cattle are given. The implication of the results with regard to the use of OF-animals and availability of laboratory drying equipment, is discussed