In order to investigate the biological effects evoked in the high power microwave fields, the numerical calculation of dosimetry for in vitro study has been carried out. The widely used 90 mm Petri dishes filled with human blood was planned to be exposed to high power mi- crowave pulses. Electric and magnetic vectors of the incident field were parallel to the surface of Petri dishes. Taking into account that according to the actual safety standards the specific absorption rate (SAR) is a basic restriction parameter for protecting against thermal effects in the risk assessment study the numerical calculation has been performed to maintain the SAR distribution in the specimen. The novel attempt of the dosimetry takes into account the calcu- lation of SAR of all frequency harmonics of the spectrum taking into consideration the function of permittivity of the medium (human blood) in the analyzed frequency range.