The spectroscopic analysis of the high molecular weight species condensed (CS) and sampled in the soot formation zone of a rich premixed ethylene flame was carried out in the uv-visible and infrared wavelength region. The absorptivities of the aromatic and tar fractions of CS, expressed in terms of oscillator strength in the 215-400nm wavelength region, showed a maximum of the absorptivity in correspondence of soot inception. Aromatic and tar species showed both aliphatic and aromatic characteristics by means of FT-IR analysis in the 2700-3400 cm(-1) region where the aliphatic and aromatic C-H stretch is detected. A quantitative FT-IR method was developed allowing the determination of the relative contribution of the aliphatic and aromatic hydrogen to the total hydrogen of the condensed species.