Summary Three clinical cases of accidental intoxication by carbon monoxide are presented, highlighting the difficulties for diagnosis and therapeutic managment. The diagnosis was done based on exposition, more than one family member with symptoms and the good response after retiring from the source. Carboxyhemoglobin (COHb) dosification was not held immediately which can explain the normal or slightly high values found. CK and CKMB were measured, being the last one high in the three cases. Cranial CT scan was performed when intoxication was severe. Treatment was based on oxigen administration. Two cases, one with loss of consciousness and one where other family members had sever intoxication, required the use of hyperbaric oxigen.