The paper presents the results of investigations on new procedures of determination of selected cleaning additives in diesel fuel. Two procedures: one-step analysis using gas chromatography with flame ionization detection (GC-FID) or mass spectrometry (GC-MS) and a two-step procedure in which normal-phase high-performance liquid chromatography (NP-HPLC) was used for preliminary separation of the additives, were compared. The additive fraction was collected using either simple elution or eluent backflush. Final determinations were performed by GC-FID and GC-MS. The studies revealed that it was impossible to determine the investigated analytes by one-step procedures, i.e. by using solely HPLC or GC. On the other hand, the use of a two-step procedure ensures reproducible results of determinations, and the limits of quantitation are, depending on the method of fraction collection by HPLC, from 1.4-2.2 ppm (GC-MS in SIM mode) to 9.6-24.0 ppm (GC-FID). Precision and accuracy of the developed procedures are compared, and possible determination errors and shortcomings discussed.