In addition to environmental and management factors, the degradation characteristics of forages are greatly influenced by both the structure and composition of cells within that structure. In particular, and even when grown under the same environmental conditions, marked difference exists between the tissue composition of C3 (temperate) and C4 (tropical) grasses. This differentiation, a reflection of their origin, is based on the photosynthetic pathways with C3 and C4 grasses using phosphoglycerate and oxaloacetate, respectively as intermediates. C3 grasses tend to have a lower cell wall content which is usually restricted to the stem component and a greater proportion of highly degradable mesophyll tissue. The possibility that C3 and C4 grasses exhibit different degradation characteristics depending on the rumen fermentative environment therefore exists. This is of major importance when it is considered that about 0.15m ha forage maize, a C4 grass, are grown annually in the UK. This study compared the chemical composition and in vitro degradative characteristics of three C3 forages, viz; grass hay (GH), wheat straw (WS) and rice straw (RS) and maize stover (MS) as influenced by incubation medium pH using a 4 x 3 factorial design. .