why php4.2.3 caches my pages?

Hi everyone, I'm using php 4.2.3 and putting the code that prevents caching. But this works in php4.1 but in 4.2.3 doesn't. I don't know if this is because I must change some directive in php.ini or if is someone that we can't change in php 4.2.3. Thanks in advance Rapha