Parameters of a 124Sb-Be neutron source used for “on-stream” elemental analysis are described. An analytical study of a basic on-stream system is given and some preliminary experimental results are compared with the calculations. The system consists of an irradiation chamber containing the 124Sb-Be source and a counting chamber with a delay line connecting the two. The unit can handle up to 7200 Ci of 124Sb which gives a thermal-neutron flux of ∼2 × 108 n/(cm2 sec) on the inside surface of the cylindrical irradiation chamber. A 13-liter irradiation chamber was found to be an optimum volume for all but very short-lived isotopes. In separate solutions, the elements Al, Hf, In, Mn, Ag, and V can be analyzed repetitively in 5 to 10 min cycles at <100 ppm using a 2.7-liter counting chamber. Calculated sensitivities for a number of elements and actual measured values for Al, Cl, Co, Hf, Mg, Na, and Cu are given.