Chronic mental illnesses (CMI) affect people’s daily lives including their thinking, functioning and emotions. These include schizophrenia, bipolar disorder and major depressive disorder, and are characterized by their perpetual and recurrent nature. There has therefore been a need to identify possible biological targets to get a deeper understanding of mental illnesses and to improve treatment and diagnosis standards. One newly studied concept is protein aggregation as a possible non-genetic cause of chronic mental illnesses. Five proteins were previously discovered to aggregate in brains of patients with CMI. Some of these have been confirmed to aggregate on their own, with a suggestion that each of them might influence the representation of a specific subtype of previously mentioned chronic mental illnesses. However, there have also been instances of co-aggregation in which case one protein stimulates the other one to aggregate. Co-aggregation represents the possibility that some or all of these proteins may interact with each other as a part of a single aggregation syndrome. EHD3 is a newly discovered aggregating protein in mental illness, a member of the EHD protein family, encoded by the EH domain-containing 3 gene. While there is not a lot known about its functions, it is believed to be one of the key regulators of endocytic transport and involved in promotion of dopaminergic transmission. In this research, we investigated the aggregation properties of EHD3 and specifically possible co-aggregation of EHD3 with TRIOBP-1 and Dysbindin 1A in mammalian cells. TRIOBP-1 is an aggregating protein involved in modulation of actin through binding to F-actin fibers, while Dysbindin 1A is involved in regulation of neurotransmitter release and brain development. Fluorescent microscope results have shown that while EHD3 aggregated both alone and in the presence of the two proteins, there was no sign of co-aggregation. Future research should focus on investigating both whether EHD3 aggregates in cells with other proteins implicated in mental illnesses, but also on whether aggregation of EHD3 and these other proteins occurs in the same patients.