The formation of compact particles from synthetic double- and triplestranded polynucleotides in water-salt solutions, containing poly(ethylene glycol) (PEG) has been investigated. CD spectra of compact particles are characterized by intense bands (positive or negative) in the region of 270 nm, compact particles being divided into two families--psi- and psi+--according to the CD band sign. The amplitude of the CD band at 270 nm increases with the increase of CPEG. Heating of a solution, containing compact particles, results in a disappearance of the CD band, the melting of compact particles as revealed by the CD method occuring prior to the melting of the secondary structure of the corresponding polynucleotide. It is concluded that intense CD bands, which are characteristic of the compact form of synthetic polynucleotides, arise (similar to the case of DNA or dsRNA) from regular arrangement of polynucleotide chains in compact particles. The question, concerning the relation between parameters of the secondary structure of polynucleotides and their belonging either to psi- or to psi+ family is discussed. The factors, which could account for the appearance of intense bands in CD spectra of compact particles are also considered.