We have adapted commercial immunoassay (EMIT®) procedures for dilantin, phenobarbital, theophylline, carbamazepine, tobramycin, disopyramide, quinidine, procainamide,N-acetyl procainamide, and mysoline to two different centrifugal analyzers (Centrifichem and Multistat) using maximum dilutions of reagents to reduce reagent costs to approximately one-tenth of that incurred using the manufacturer's protocol. This savings due to the dilutions of reagents was primarily because of the ability to prolong the reaction time to achieve acceptably large absorbance changes over the absorbance measurement period. Correlation coefficients between values for drugs analyzed by these modified EMIT protocols and values obtained by other methods ranged from 0.927 to 0.994. Within-run precision and recovery values for these drugs were also entirely acceptable. We found that premature mixing of reagents in the rotors of the Multistat system and variable delivery of reagent in the Centrifichem 400 system were both caused by the surfactant in the EMIT buffer. The former problem is being resolved by the manufacturer; the latter problem was resolved by siliconizing the reagent pipet tips.