Guidor is an NPC that can be found in southeastern Varrock. He tests the plague sample for you during the Biohazard quest. He has a wife whose also featured in the quest. Being a religious person she will only let a priest, or a player dressed as one with a Priest robe and Priest gown, in through the door to cure Guidor in the Biohazard quest.
Players who have not started the Biohazard quest will receive no message when attempting to open the door, other than that it is locked.
For players who have started or completed the quest, attempting to enter Guidor's room without being dressed as a priest receive the message: guildors wife refuses to let you enter[sic]