You didn't say what type you were referring to, however I'll assume it was one of the more common types.
I have found from time to time my Chameleon needs to be placed in a tepid shower for approximately 20 minutes. Whilst he is spayed and does have access to a dripper I don't believe he hydrates himself enough. When in the shower he will start to open his mouth and allow the water droplets to run down his throat. The first time I did this I was surprised at how thirsty he really was. There is plenty advise on Chameleon Forums on how to successfully shower a Chameleon.
I hope this works for you.