Аннотация:As low detection limits for lithium and cesium as 3x10-5 and 1x10-4 ppm respectively were achieved by step atom ionisation in flames. The mobilities of lithium and cesium ions in flame were measured (17.0+/-3.2 and 10.1+/-2.1 cm2/v*sec respectively). It has been shown by calculation that minimum atom concentrations, that can be measured ifn flame by step atom photoionization, are 10-4 - 10-6 atom/cm3.