The aim of this study was to evaluate the effect of four different storage media on the elution of monomers from two composite materials. Samples (n = 10, diameter: 4.5 mm, thickness: 2 mm) of two different composite materials (Ceram X™ & Filtek™ Supreme XT) were stored after polymerization in four different media (NaCl, saliva, ethanol 75% & acetone) for 24 h, 7 days, and 28 days. From the storage medium of each tested time period, samples were prepared and analyzed by LC-MS/MS, for the elution of BisGMA, TEGDMA, HEMA, Bisphenol A, and two types of UDMA. No monomers were detected in the samples of Ceram X™, independently of the storage medium used. In the samples of Filtek™ Supreme XT, no Bisphenol A, HEMA, and UDMA 1 were found. BisGMA was detected only in the ethanol and acetone samples. The amount of BisGMA eluted in acetone was significant higher compared with ethanol 75% (p < 0.0001). TEGDMA was the only monomer that could be detected in all tested storage media. Storage in acetone resulted in higher release of TEGDMA when compared with other media. The amount of TEGDMA released in saliva was similar to the one released in ethanol 75%. It can be concluded that acetone is not a suitable medium for elution experiments and although ethanol 75% can simulate saliva concerning the elution of TEGDMA, it does not represent a laboratory substitute of saliva with respect to the elution of monomers like BisGMA.