The solution properties of a N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing Zn(II) 4,9,16,23-tetraaminophthalocyanine (HPMA-TAPC-Zn copolymer) attached to the copolymer via oligopeptide side chains (GFLGG) were studied using light scattering and spectroscopic methods. The light scattering data indicated that the copolymer formed aggregates in aqueous solutions stable down to c = 2 x 10(-5) g/mL. The extent of aggregation decreased with increasing concentration of detergents in buffer solutions or organic solvents in mixed solvents as Tris buffer/DMSO. Dramatic changes in the aggregate formation were observed in the vicinity of a mixture composition of 60 vol % of DMSO. The local interactions of hydrophobic TAPC-Zn species were studied by absorption and fluorescence spectrometry. The majority of all TAPC-Zn species are dimerized in aqueous solutions by hydrophobic interactions and hydrogen bonds. The proportion of TAPC-Zn monomers and dimers estimated for Tris buffer/DMSO mixtures from both the absorption and fluorescence spectra was correlated to the aggregation behavior of the copolymer : The copolymer aggregation was explained by the random association model. Mostly point-like contacts formed by TAPC-Zn dimers are supposed for aqueous solutions of HPMA-TAPC-Zn copolymer.