ABSTRACTThe seasonal pattern of DM prodaction ofLolium perenne, Cynosurus cristatus. Anthoxanthum odoratum. Festuca ovinaandAgrostis stolonifera. cnt to 3 cm at 6‐week intervals was studied on five sites, ranging from 49 to 303 m above sea level, in north‐west Lancashire. Total annual production declined from a mean of 704 g/m2on the lowest site, to 553 g/m2on the highest, largely as a result of a severe depression in the spring peak of production, i.e. from 6.7 to 2.5 g/m2per day. Later in the year, the daily rate of DM production was similar on all sites. Species varied in their response to increased altitude;Loliumwas worst affected by this andFestucaleast. The significance of these results, and possible reasons for the decline in spring production are discus