Time-resolved fluorescence anisotropy (FA) measurements are reported for 5 helical, bilayer-spanning heneicosapeptides, each contg. 1 tryptophan (Trp) at sequence positions 1, 6, 11, 16, and 21, resp. The FA decay reflected 2 mol. processes in all cases, local internal fluctuations of the Trp side-chain with a relaxation time of 200-500 ps and motions of the whole polypeptide mol. with a relaxation time of 9-10 ns. Concomitant mol. dynamics calcns. indicated a correlation between the fast FA decay and conformational fluctuations within the helix. [on SciFinder (R)]