In order to examine the relationship between herbage maturity and methane (CH(4)) emission under conditions which minimized opportunities for selective grazing, six 8-yr-old, dry and early-pregnant Charolais cows [712 +/- 22.7 kg liveweight (LW)] were grazed on a mono-specific pasture of timothy at four stages of maturity: early vegetative, heading, flowering, and senescence. Daily CH(4) production was measured during 7 d using the sulfur hexafluoride (SF(6)) tracer-gas technique. Organic matter intake (OMI) was determined from fecal output estimated by Yb(2)O(3) dosing and feed digestibility (OMD) estimated using a fecal N index. The OMD (%) decreased (P < 0.05) from 77.6 at early vegetative to 56.2 at senescence, but no cow effect upon OMD was observed. The OMI (14.8 g kg(-1) LW) and CH(4) production (273 g d(-1)) were higher (P < 0.05) at heading than at the other stages of maturity. The proportion of gross energy intake (GEI) lost in CH(4) did not differ with maturity (mean 6.4% of GEI). Cow effects upon OMI and CH(4) emission-were significant (P < 0.05). CH(4) production (g d(-1)) was not related to diet chemical composition or OMD, but was correlated with digestible neutral detergent fiber (NDF) intake (kg d(-1)) (r = 0.61, P < 0:01). Across all stages of maturity between-cow variation explained 54 to 70% of the total variation in CH(4) production.