Summary: Homogeneous enzyme immunoassay reagents (EMIT) developed for the measurement of amitriptyline and nortriptyline in serum were modified to allow quantitation of clomipramine and desmethylclomipramine. The method was compared to a high-performance liquid chromatographic method. Between-run precision [coefficient of variation (CV)] for clomipramine in the EMIT assay for amitriptyline ranged from 2.6 to 3.2%. For desmethylclomipramine in the nortriptyline assay, the between-run CV ranged from 1.4 to 1.9%. Serum specimens from 43 patients (desmethylclomipramine) and 59 patients (clomipramine) were analyzed by both methods, with good correlation between methods. For clomipramine, recovery ranged from 100 to 102% (0–600 ng/ml range) and was 95–103% for desmethylclomipramine (0–600 ng/ml). The modified EMIT assays offered sufficient reproducibility, accuracy, and correlation with an established method for routine analysis of clomipramine and desmethylclomipramine.