The US Department of Energy needs improved analytical methods for alpha-emitting radionuclides to support environmental restoration and waste management projects. Inductively coupled plasma-mass spectrometry (ICP-MS) has been used successfully to measure radionuclides with relatively long half-lives; however, ICP-MS used with conventional sample introduction techniques lacks the sensitivity or selectivity to measure shorter-lived radionuclides at levels important for environmental monitoring. New methods were developed for measuring ²³⁰Th, ²³⁴U, ²³⁹Pu, and ²⁴⁰Pu in soils. Samples are dried, ground, and dissolved by fusion. A flow injection (FI) analysis system is used to separate and concentrate the analytes by solid-phase extraction. The FI eluent is pumped directly into the nebulizer of the ICP-MS. The use of FI resulted in greater sensitivity and freedom from interferences when compared with direct aspiration. Detection limits are improved by approximately a factor of 20. The detection limits are approximately 3 Bq/kg (4 ng/kg) for ²³⁰Th, 0.6 Bq/kg (3 ng/kg) for ²³⁴U, 0.4 Bq/kg (0.2 ng/kg) for ²³⁹Pu, and 2 Bq/kg (0.3 ng/kg) for ²⁴⁰Pu. The FI-ICP-MS methods are faster, less labor intensive, and generate less laboratory waste than traditional radiochemical methods. The FI-ICP-MS gives individual results for ²³⁹Pu and ²⁴⁰Pu which cannot be resolved by the usual radiochemical method. The accuracy of the methods was verified by analyzing reference soils.