Metacognitive variables influence students' learning from science texts. This article deals with the comprehension monitoring abilities of secondary school science students, one of the areas of metacognition which has drawn considerable attention from researchers. The aims of the study are, in particular: (a) to know the extent to which comprehension is monitored by secondary science students as revealed by inconsistency detection in manipulated science texts, and (b) to identify the strategies used to regulate comprehension by the students who detect the inconsistencies. The results indicate that knowing that one understands or fails to understand science texts could be as important a problem as understanding proper. Besides, some incorrect regulatory strategies used by students who notice the inconsistencies in the texts are identified. These could also have an annoying influence in the regulatory behavior of students when studying regular science texts.