Arrest, detention, and bail procedures, prescribed in the country's Criminal Procedure Code of 1935, are delineated. The statistics provided indicate that in 1978, 93.90 percent of all crimes reported to the police resulted in arrests, and 23.40 percent of the total prison population consisted of pretrial detainees (10.64 percent), those awaiting trial detention (12.07 percent), and those detained pending appeal (0.69 percent). The text also discusses the propriety of arrest and detention as presented in the Constitution of the Kingdom of Thailand and the Criminal Procedure Code, which protect persons from being illegally arrested and detained, and in the Communism Prevention Act of 1952. Measures for preventing prolonged and illegal detention are also considered. Finally, the treatment of arrested or detained persons receives attention in view of efforts by the Department of Corrections to provide adequate living conditions and to protect the basic human rights of detainees, as specified in the United Nations rules for the treatment of prisoners. The paper concludes with a call for the increased use of bail and for speedier investigations and trials to reduce the number of detained persons. A reference list is not included.