The simultaneous serum analysis of amoxapine (AMOX) and its major metabolite 8-hydroxyamoxapine (8-OH AMOX), and maprotiline (MAP) and its major metabolite desmethylmaprotiline (D-MAP) by high-performance liquid chromatography (HPLC) and ultraviolet detection is described here. AMOX and 8-OH AMOX were detected at 254 nm at 0.01 absorbance units full scale (AUFS). MAP and D-MAP were detected at 214 nm at 0.05 AUFS. Serum (1.0 ml collected in plastic) extraction was by Bond-Elut C18 columns. The compounds of interest were eluted from the columns with 10 mM methanolic ammonium acetate. The eluates are evaporated at 56-58 degrees C and reconstituted with 200 microliter of mobile phase. The mobile phase was absolute ethanol-acetonitrile-tert-butylamine (98:2:0.05, vol/vol), and the flow rate was 2.0 ml/min. Absolute recoveries range from 97 to 100% for all compounds. HPLC was done on a 5-micron (4.6 X 250 mm) silica-packing column (normal phase). Separations on a 10-micron silica column (3.9 X 300 mm) are also discussed. Peak height ratios using trimipramine as the internal standard were linear for each drug between 25 and 1080 ng/ml. AMOX and 8-OH AMOX ratios with promazine as the internal standard were linear between 25 and 1080 ng/ml. Detection limits were 3 ng/ml for AMOX and 8-OH AMOX, 12 ng/ml for D-MAP, and 15 ng/ml for MAP. Coefficients of within-day and day-to-day variation at three concentration levels were less than 10.8% and 10.5%, respectively, for all compounds. Correlations of AMOX, 8-OH AMOX, and MAP sample assays using gas chromatography (or gas chromatography-mass spectrometry) and this method were compared. Steady-state daily dosages and corresponding serum levels are presented for seven patients. AMOX and 8-OH AMOX concentrations for 37 patients are given; these show that the ratios of these compounds are highly variable between patients. MAP and D-MAP concentrations for 30 patients show that D-MAP can be a significant fraction of the circulating drug. Assay time for 8-OH AMOX/AMOX was 6.5 min and less than 13 min for D-MAP/MAP.(ABSTRACT TRUNCATED AT 250 WORDS)