The present investigation uses the methodology of Conversation Analysis to study the particle ah in Mexican Spanish interactions. It looks at ah as a change-of-state token in remembering and noticing sequences. Similar to previous studies (e.g., Edwards and Middleton 1986; Goodwin 1987; and Drew 1989), this investigation aims to show how cognitive processes are socially organised in interaction. Three types of remembering sequences are identified and described: assisted, metacognitive, and spontaneous remembering. It is suggested that in these type of sequences, ah marks the end of the cognitive process which is completed either with external help or with metacognitive strategies. In noticing formulations, ah marks the realisation of something, it prefaces a noticing formulation which may work as a topic initiator or it may initiate the closing of a sequence. A noticing formulation may also work as an account of action.