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Selectivity by cattle for the more important species in their diet and the effect of stocking rates on species selectivity were determined in spring, summer, and fall-winter during a 3-year period. The selection index ((% diet- % available in field)/(% diet + % available in field)) x 10 was calculated. Grasses were classified as preferred: Chloris castilloniana, Digitaria californica, Sporobolus cryptandrus, and Pappophorum philippianum, the latter only in spring and summer; proportional: Panicum urvilleanum; variable: Setaria leucopila; and rejected: Aristida sp. Most of the woody species were avoided in summer and had higher selectivity in spring and fall-winter. Several species tended to be more highly selected as stocking rates increased. (C) 1996 Academic Press Limited