The annual growth and biomass cycle of Cymodocea nodosa (Ucria) Ascherson in the Mar Menor lagoon (southeast Mediterranean coast of Spain) during 1988-1989 is described. Leaf growth was estimated by the hole punching method; rhizome production was assessed by marking rhizome extremes and dating meadow biomass. Cymodocea nodosa meadows show a clear unimodal growth cycle. reaching maximum leaf development in summer. Rhizome growth is maximum in late spring and stops from October to January. Leaf production was 160-164 g dry weight (dw) m-2 year-1 (47.7-48.9 g C m-2 year-1; production/biomass ratio (P/B) = 2.36-2.57 year-1) in the meadow on sand, and about 290-427 g dw m-2 year-1 in the meadow on mud. Rhizome production was 46-48 g dw m-2 year-1 (15.2-15.8 g C m-2 year-1; P/B=0.27-0.31 year-1) in the meadow on sand, and about 66-78 g dw m-2 year-1 in the meadow on mud.