A non-clairvoyant scheduler makes decisions having no knowledge of jobs. It does not know when the jobs will arrive in the future, that is. it is online, and how long the jobs will be executed after they arrive. For non-clairvoyant scheduling, we first study the problem to minimize the total stretch. And we also consider the case in which the weights of jobs are known when they arrive, while their lengths are still unknown. In this case, we find a schedule to minimize the total weighted flow time. The weighted versions of well-known algorithms, Round Robin and Balance, are investigated. (C) 2003 Published by Elsevier Science B.V.