Analytical procedures have been developed for the determination of the allylamine antimycotic terbinafine (1) and its demethylderivate (2) in plasma, milk and urine, and the metabolite carboxy-terbinafine (3) in plasma and urine, as well as the further metabolites demethyl-carboxy-terbinafine (4) and naphthoic acid (5) in urine. HPLC-methods for plasma analysis employed either electrochemical detection (for 1 and 2) or UV-detection (for 3) following a protein precipitation step with methanol or sample extraction with hexane as appropriate. For quantitative urine analysis of substances 1-4 native urine samples were deconjugated, mixed with internal standard and injected by an autosampler into a microprocessor controlled HPLC-system. The substances were monitored by UV-absorption. The metabolite 5 was determined in urine after deconjugation, sample preparation with commercially available cartridges and silylation by automatized GC with fused silica capillary column and FID-detection. The standard calibration curves for the parent compound (1) and metabolites (2-5) are linear within the required analytical ranges. The detection limit for 1 and 2 is 50 ng/ml in plasma and 150 ng/ml in milk and for 3 in plasma 100 ng/ml. The detection limit in urine is 300 ng/ml for all substances (1-4) analyzed by HPLC and 50 ng/ml for 5 analyzed by GC.