Phenemal, phenytoin and carbamazepine were determined by the EMIT method on an LKB 2086 Reaction Rate Analyzer and the results compared with routine results obtained for phenemal by gas chromatography and for phenytoin and carbamazepine by thin layer chromatography. Coefficients of variation for phenemal at the concentration 99 mumol/l in bovine serum were 3.1% within run and 10.8% between run. For phenytoin the coefficients of variation were respectively 13.1% and 15.4% for the same serum with a concentration of 99 mumol/l. For carbamazepine the coefficients of variation were estimated to be 14.1% within run and 10.4% between run for a human serum containing 25 mumol/l. With an LKB 2082 Kinetic Data System the coefficients of variation phenytoin and carbamazepine were reduced to 8% and the coefficients of correlation between the EMIT methods and the routine methods were at least 0.965 for all three drugs. The assay ranges were found to be satisfactory. The method allows assay down to 8.6, 4.0 and 2.1 mumol/l and up to 301, 198, and 51 mumol/l for phenemal, phenytoine and carbamazepine, respectively.