The fluorescent peptidocalixarenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(O-methyl-L-tryptophanylcarbonylmethoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-di(O-methyl)-26,28-bis(O-methyl-L-tryptophanylcarbonylmethoxy)calix[4]arene (2), were prepared by introducing tryptophan subunits at a lower calixarene rim. Coordination abilities of 1 and 2 towards Eu(III) and alkali metal cations were studied by spectrophotometric, spectrofluorimetric, conductometric and potentiometric titrations in acetonitrile at 258C. Rather strong complexation was observed for smaller alkali metal cations Li þ and Na þ (log K Li1 . 6, log K Li2 . 6, log K Na1 ¼ 8.25, log K Na2 ¼ 6.94), and moderate for K þ (log K K1 ¼ 5.09, log K K2 ¼ 4.09). Larger Rb þ and Cs þ cations did not fit in the ion binding site of 1 so no complexation was detected, whereas the more flexible ligand 2 accommodated Rb þ cation (log K Rb2 ¼ 3.44). The fluorescence of 1 (l ex ¼ 280 nm, l em ¼ 340 nm) was remarkably quenched by Eu(III). Stability constant of 1:1 (Eu 3þ :1) complex determined spectrofluorimetrically amounted to log K Eu1 ¼ 6.16.