[en] Thymidine incorporation by the microbial community on standing dead leaves of Spartina alterniflora did not obey many of the assumptions inherent in the use of the technique in planktonic systems. Incorporation rates of [methyl-³H]thymidine were nonsaturable over a wide concentration range (10¹ to 10⁵ nM). Owing to metabolism by both fungi and bacteria, a major fraction of the radiolabel (mean, 48%) appeared in protein. Extraction of the radiolabeled macromolecules were inefficient, averaging 8.8%. Based on an empirically derived conversion factor, 4 x 10¹⁸ cells mol of thymidine^-1, doubling times ranged from 4 to 69 h for the epiphytic bacterial assemblage