SUMMARY1 Phosphorus enrichments of 5 weeks' duration were performed in two woodland streams in eastern Tennessee, U.S.A. to determine their effect on the dominant stream bryophyte,Porella pinnata.2 In a second‐order reach of Walker Branch, which had an N:P ratio (by atoms) of 3.5:1 in the stream water, the P:C ratio ofPorellawas not significantly affected by enrichment, but the P:N ratio did increase significantly. In Sludge Creek, which had an N:P ratio of 21.6:1 in the stream water, both P:C and P:N ratios ofPorellaincreased significantly following phosphorus addition. Increased phosphorus ratios may have resulted from either assimilation or adsorption.3 Absolute phosphorus concentrations inPorellatissue were significantly greater prior to enrichment in the control reach of Walker Branch, confounding the effect of phosphorus enrichment. In Sludge Creek, absolute phosphorus content inPorellatissue increased significantly in the treated reach and showed no significant difference in the control reach.4 Although mean primary production increased by approximately 15% following enrichment, the increase was not significantly different from that prior to enrichment.5 Epiphyte structure and abundance were not significantly influenced by enrichment in either stream. It is suggested that grazing pressure by snails may have masked any potential epiphyte response to