The evaluation of capabilities of thermal ionization mass spectrometry in trace analysis of U, Np, Pu, Am in samples without preparatory extraction/purification procedures is presented. The total evaporation method was used along with multichannel ion detection in the ion counting mode. In soil ashes extracts, the detection threshold of Pu was found at concentrations of about 1 ppt. In dissolved metal microsamples, U concentrations were determined in the range 0.02–0.2 ppb (3–110 ppb in analysed metal). The detection threshold of actinides in purified liquid microsamples (1–5 mkl) was estimated to be about 0.1 ppt.