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Objective: Previous studies documented that there were a variety of endophenotypes that helped to diagnose as well as to predict functionality and treatment response. There is little, if any research that focused on investigating biochemical endophenotypes. Besides, the studies that include executive functions and social cognition, which were accepted as endophenotypes, have different results. In studies involving schizophrenia patients, the deficiency of oxytocin was found to be the most important hormone that would affect the treatment process. However, there have been no endophenotype studies that investigated the role of oxytocin hormone in the treatment process of schizophrenia patients. The purpose of the present study was twofold: (a) to detect new endophenotypes, and (b) to test endophenotypes that were previously found by focusing on the schizophrenia patients mothers. Methods: The participants were the healthy mothers of schizophrenia patients and healthy control group. They took the Reading the Mind in the Eyes Test, Wisconsin Card Sorting Test, and Wechsler Adult Intelligence Scale vocabulary subtest, respectively. In addition, participants blood samples were collected to include the level of plasma oxytocin as a biochemical in the data analyses. Results: Results revealed that there was a significant difference in plasma oxytocin levels for the healthy mothers of schizophrenia patients and the healthy control group. Low level of plasma oxytocin level was found to be the only significant factor that differentiates the patients mothers and the healthy control group. When the results of the Reading the Mind in the Eyes Test that measures executive functions, and the Wisconsin Card Sorting Test that measures social cognition were analyzed, no significant differences were found between the groups. Discussion: Our findings showed that oxytocin hormone could be a new endophenotype for schizophrenia. However, there is still a need for studies that focus on the investigation of detecting new endophenotypes. [Anadolu Psikiyatri Derg 2017; 18(4.000): 307-313]