A high-performance liquid chromatographic method using a fluorometric detector was developed for the determination of plasma concentrations of the antidepressant indalpine (I) and its major metabolite 4-[2-(3-indolyl)ethyl]-2-piperidinone (PK). the same procedure was used to measure, in urine, levels of I and of the metabolite, either conjugated or unconjugated. The sensitivity of the assay is 5 n g mi-' of plasma or urine for both I and PK. Mean recoveries from plasma for PK, I, and the internal standard (quinine sulfate) were 86.4, 8 6 4 , and 88.5 per cent, respectively. Mean recovery from urine for I was 82.5%. This method was used to establish the pharmacokinetic profiles of I and PK following a single oral administration of I (100rng) in 8 healthy volunteers. Peak plasma concentrations for I and PK were obtained in an average time of 2.1 and 2.6 h (tmex), respectively. The mean absorption tlh of I was 0.8 h, the mean V,, 878 1 and the mean clearance 58 1 h-'. The mean t& for I and PK was 10.4 and 11.9 h, respectively. In a 12 h urine collection 3 per cent of I was excreted unchanged. No conjugated or unconjugated metabolite was found in urine samples. This method was also used to determine plasma levels 10 h post-dose (50mg t.i.d.) during chronic oral administration in 20 hospitalized patients. Mean plasma concentrations of I and PK post-dose were 116ng ml-' and 43ng ml-', respectively.