This paper discusses the use of trap-and-release membrane inlet mass spectrometry (T&R-MIMS) for the quantitative determination of semivolatile organic compounds in real samples. We found that the T&R-MIMS technique is particular sensitive to relatively polar, semivolatile organic compounds. For example, the detection limits for the acids acetylsalicylic acid and phenoxyacetic acid were lowered by a factor of 100 as compared with those possible with standard MIMS, and caffeine was detectable only with the T&R-MIMS method. The detection limits were in the parts-per-billion range, and the dynamic range was 3 orders of magnitude. As a practical example of the application of the T&R-MIMS technique, we used it for the quantitative analysis of caffeine in ground coffee and tea leaves. Good agreement between T&R-MIMS and HPLC determinations was found, and the reproducibility of the whole analytical system for caffeine determination (extraction procedure and T&R-MIMS determination) was within 10% as relative standard deviation. However, for coffee, a large background from the essential oils prevented low-level work, such as the determination of residual caffeine in decaffeinated coffee. Obviously, the analysis of many complex matrixes will require the use of tandem mass spectrometry.