The process of elution of unreacted monomers from dental resin composites can adversely affect their biocompatibility and longevity. In this regard, it is of interest to monitor relies on unreacted monomers from SonicFill, especially since this new type of bulk-fill composite materials entered dental practice with their simplified and shortened application protocol. This study aimed to assess long term monomer elution from bulk- fill (SonicFill) and conventional low shrinkage resin composites (FiltekP60 and FiltekUltimate), applied in 2mm layer thickness and stored in different extraction media - 6-month period exposure in artificial saliva, followed by 24 hours exposure in 75% ethanol solution. Analysis of monomer elution was performed using HPLC-MS. Monomers detected in artificial saliva were: UDMA and EDB from the conventional composites. No eluted monomers were detected from SonicFill. In just 24 hours of exposure in 75% alcoholic solution, components were extracted from all the materials that were not extracted for 6 months in the artificial saliva: Bis-GMA, TEGDMA, EDB from SonicFill; Bis-GMA from Filtek P60, and Filtek Ultimate. There was a new peak in the release of UDMA from Filtek P60 and Filtek Ultimate. Data reveal, that the extraction medium is extremely important for the separation of monomers. The degree of polymerization cannot completely influence the release of monomers into the surrounding environment. Internal factors, concerning materials composition, are more important, than the ability to control clinically degree of polymerization by intensity and duration of light exposure.