The simultaneous determination of betaine (trimethyl-glycine), N,N-dimethylglycine (N,N-DMG), acetic, and propionic acid in complex organic matrices for process monitoring is described. In some cases also ammonia and chloride were detected. The determinations were carried out by means of isocratic cation-exchange chromatography. For the detection of betaine and N,N-DMG an ultraviolet detector was used. All other substances were detected by conductivity. Linear calibration curves were obtained for betaine (0.01-7.71 g/l), both organic acids (0.06-60 mM), chloride (0.01-4.31 g/l), and ammonia (0.05-1.02 g/l) over the concentration range given in parentheses. The results obtained by HPLC were checked by gas-chromatographic (GC) measurements for the organic acids and by photometric tests for betaine and ammonia. The values for the organic acids obtained by HPLC and GC varied only in the range of the statistical deviation of the two methods. A larger discrepancy was observed for betaine. The values obtained after precipitation of betaine as a reineckate were up to 60% higher than those of the HPLC measurements. The results of the two methods were the same if the samples were filtered through a microporous membrane with a cut-off of 20 kDa. The applicability of the HPLC method for online process monitoring was shown in the context of an experiment being run for 40 h.