The aim of this study was to describe the excretory–secretory proteins from the helminth Schistocephalus solidus and its intermediate host, the three-spined stickleback Gasterosteus aculeatus L., which are likely to be involved in interactions between them. Combined samples of washes from the G. aculeatus sticklebacks cavity infected with the S. solidus, and washes from the parasite surface were used as experimental samples (samples 5 to 8), while washes from the uninfected fish body cavity were used as control (samples 1 to 4). The obtained samples were analyzed using mass-spectrometry nLC–MS/MS.