We investigated a method for the simultaneous screening, identification, and quantitative determination of salicylic acid, acetaminophen, theophylline, barbiturates, and bromvalerylurea, drugs that frequently cause acute poisoning in Japan and therefore require rapid analysis for effective treatment in the clinical setting. The method employs liquid chromatography/electrospray mass spectrometry (LC/MS) of solid-phase extracted serum samples. For LC/MS ionization, the electrospray-ionization method was used, with acetaminophen in the positive-ion mode, and salicylic acid, theophylline, phenobarbital, bromvalerylurea, pentobarbital, amobarbital, and o-acetamidophenol (internal standard) in the negative-ion mode, the base ions were used in each case for quantitative analysis. Quantitation was possible for the following sample concentration ranges: salicylic acid and acetaminophen, 100 to 5 μg/ml; theophylline, 100 to 0.5 μg/ml; and phenobarbital, bromvalerylurea, pentobarbital, and amobarbital, 100 to 1 μg/ml. Using full-scan mass spectrometry, the lower detection limits of 1 μg/ml for salicylic acid and acetaminophen, 0.1 μg/ml for theophylline, and 0.5 μg/ml for phenobarbital, bromvalerylurea, pentobarbital, and amobarbital were adequate for identifying acute poisoning. When each compound was added to serum to a final concentration of 5 μg/ml and solid-phase extraction was performed using Oasis HLB 1-cc (30-mg), the mean recovery rate of each compound was 89.2 to 96.1% (n=5), and the coefficients of variation of the intraday and interday assays were 3.55 to 6.05% (n=5) and 3.68 to 6.38% (n=5), respectively, which are acceptable. When this method of analysis was applied in testing the sera of a female patient who had consumed a large amount of an unknown commercial drug, salicylic acid and bromvalerylurea were identified, and the treatment strategy could be determined in accordance with the serum concentration of those drugs.