Adding circuit in existing EMT?

I'd like to have a copy of the NEC, but I cannot justify the expense of buying the big book for the little bit I would use it.

I would like to pull a new 120V branch circuit through an existing 3/4" raceway which is currently housing only the conductors for a 240V electric dryer.

Is there any reason I should not do this?

Unless there is something unusual about your conduit it would be OK.