Carisoprodol (CSP) is a musculoskeletal relaxant whose active metabolite is meprobamate (MPB). This drug has recently been noticed to be abused as an inexpensive alternative to illicit drugs in Korea. A method using solid-phase extraction (SPE) and gas chromatography/mass spectrometry (GC/MS) was developed for the determination of CSP and MPB in human hair. Hair samples (30 mg) were washed with distilled water and acetone, cut into small fragments (<1 mm), incubated in 1.0 M HCl overnight at 50 degrees C, and then adjusted to pH 6.5. The drugs were extracted from the resulting hydrolyzed solutions using a SPE column. The eluents were evaporated to dryness, then derivatized using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS) at 120 degrees C for 30 min. The derivatized extract (1 microL) was injected into the GC/MS system. Recoveries were in the range of 91.5-93.1% for CSP and 85.5-93.0% for MPB. The linear ranges were 0.5-10.0 ng/mg for both CSP and MPB with good correlation coefficients (r(2) = 0.995). The intra-day precision and accuracy ranged from 1.5 to 9.3% and -17.5 to 3.6%, respectively, and the inter-day precision and accuracy ranged from 3.9 to 6.2% and -15.0 to -3.9%, respectively. The limits of detection for CSP and MPB were 0.13 and 0.12 ng/mg, respectively. The applicability of the method was proven by analyzing a hair sample from an authentic abuser.