A novel and simple high-performance liquid chromatography method has been developed for the simultaneous determination of two selective serotonin reuptake inhibitors (fluoxetine and paroxetine) and two serotonin-norepinephrine reuptake inhibitors (venlafaxine and duloxetine) in alternative samples of toxicological interest such as hair, nail clippings, and cerebrospinal fluid (CSF). The separation was achieved on a Hichrom Kromasil 100-5C(18) (250 × 4.6 mm) 5 μm column by using ammonium acetate (0.05 M)-acetonitrile (59:41% v/v) as the mobile phase, delivered isocratically at a flow rate of 1.3 mL/min, within ca. 10 min. Ultraviolet detection at 235 nm was used for monitoring the eluting analytes. Validation was performed in terms of linearity, selectivity, accuracy, precision, and stability. Correlation coefficients were greater than 0.9954. The limits of quantitation ranged between 0.3 and 2.1 ng/μL for all analytes in the liquid matrix (CSF), while the respective values were in the range of 0.3-3.6 ng/mg for solid matrices (hair and nail clippings), with an injection volume of 20 μL. Repeatability and intermediate precision (relative standard deviation, RSD%) were less than 16.6%. The method was successfully applied to actual hair and nail samples from a patient under fluoxetine treatment.