The interactions between polycationic poly-lysine dendrimers and hydrophobic fluorescent probes (anionic ANS and neutral Prodan) were studied. R121 and R131 dendrimers were not able to interact with anionic and neutral hydrophobic groups. R124 was able to interact with neutral and anionic hydrophobic fluorescent probes, however mainly through hydrophobic forces. Dendrimers R155 and R169 showed the maximal effects. The strongest interactions observed for R169 can be explained by intramolecular folding (stacking) of its two L-proline residues. Using double fluorescence titration technique for ANS probe allowed to receive such constant of binding and the number of binding centers: for R121, 1.8 x 10(3) (mol/l)(-1) and 1.07; for R124, 12.1 x 10(3) (mol/l)(-1) and 0.48; for R131, 4.7 x 10(3) (mol/l)(-1) and 0.48; for R155, 9.2 x 10(3) (mol/l)(-1) and 1.36; for R169, 39.6 x 10(3) (mol/l)(-1) and 0.97. Thus, neutral and anionic hydrophobic probes can be used for the fast preliminary screening of binding properties of newly synthesized polycationic dendrimers.