A simple, rapid, reliable, and low cost one-step extraction method is developed and validated for the determination of nicotine and cotinine in human plasma and urine in smokers using reversed-phase high-performance liquid chromatography (RP-HPLC) and gas chromatography-mass spectrometry (GC-MS). The run times are 16 and 10 min for HPLC and GC-MS, respectively. The method is validated over a wide linear range of 1–5000 ng/mL with correlation coefficients being consistently greater than 0.9985. The criteria considered for validation are: limit of quantitation, linearity, accuracy, precision, recovery, specificity, and selectivity. This study is aimed to estimate the nicotine and cotinine in Jordanian smokers' blood and urine samples; to study the relationship between the concentration of nicotine in urine and plasma samples; and to investigate the effect of pH on the extraction of nicotine and cotinine in urine samples. In the presented study, one hundred blood and urine samples are collected from eighty smokers and twenty nonsmokers. Samples are taken from the same volunteer at the same time after each volunteer fills in a questionnaire. Results of nicotine concentrations in smokers' plasma are in the range of 181–3702 ng/mL with an average of 1263.1 ng/mL, whereas nicotine in urine samples is in the range of 1364–1972 ng/mL, with an average of 1618 ng/mL. Cotinine concentrations in smokers' plasma are in the range of 21–4420 ng/mL with an average of 379.4 ng/mL, whereas cotinine in urine is in the range of 6–3946 ng/mL with an average of 865 ng/mL. Statistical analysis indicates highly significant differences in nicotine and cotinine concentrations in smoker samples compared with nonsmoker samples (p < 0.05).