Study of D0-D-bar0 mixing.

We present a study of D0 mixing using events of the type D*+→π+D0, with D0→K+π− and D0→K+π−π+π−. The decay time is used to separate mixing from doubly Cabibbo-suppressed decays. We observe no evidence for mixing in either mode. Combining the results from the two decay modes, we find rM=0.0005 ±0.0020 or rM<0.0037 at the 90% confidence level, where rM is the ratio of wrong-sign decays from mixing to right-sign decays. We also present limits on doubly Cabibbo-suppressed decays and consider the effect of possible interference.