Memcache::replace Replace value of the existing item boolMemcache::replace stringkey mixedvar intflag intexpire Memcache::replace should be used to replace value of existing item with key. In case if item with such key doesn't exists, Memcache::replace returns &false;. For the rest Memcache::replace behaves similarly to Memcache::set. Also you can use memcache_replace function. See example below. replace("test_key", "some variable", false, 30); ?> ]]> &return.success; See also Memcache::set, Memcache::add.