$_SESSION and header()

(a) : After saving a couple of data into two $_SESSION variables from a form, (b) : I used the header() function to redirect the browser to (c) : display another page. But, when I'm in the new page of (c), the $_SESSION variables stored in (a) are no longer available and I can get anymore their values then, (I can't say if they have been unset or erased). I presume there's some relation with the use of header() and the lost data. My intention is to keep the automatic redirection by the header(). Any suggestion? Thanks in advance. Alessandro Rosa