Studies of tannin concentrations in forage plant species in arid south-eastern Spain were conducted to assess the relationship between tannins and use of plants by domestic livestock. Tannin concentrations were measured in the most important forage plants (28 shrub species and 12 herbaceous species) in each of the four seasons of the year. Twenty-five percent of the shrubs were rich in tannins. The shrubs, Helianthemum almeriensis and Dorycnium pentapyllum, had the highest concentrations of tannins (4·5% and 4·0% in dry matter, respectively). With the exception ofSedum sediforme , herbaceous species had no tannins.