To investigate the formation of precipitation between various intravenous agents, we cross-matched the anesthetic agents commonly used in the induction phase. Thiopentone and thiamylal precipitated in combination with non-depolarizing muscle relaxants, lidocaine, morphine, and meperidine. Ketamine and etomidate were naive to these agents. Crystalloidal solutions, such as lactated Ringer, normal saline, and dextrose solution did not contribute to the formation of precipitate. In conclusion, our study indicates that intravenous line must be irrigated before and after thiopentone and/or thiamylal. In order to prevent precipitate formation, mixtures of various drugs should be avoided until in vitro assay is done.