ADEVA, B (reprint author), CERN, EUROPEAN LAB PARTICLE PHYS, CH-1211 GENEVA 23, SWITZERLAND.
A more precise determination of the B0-B0BAR mixing parameter in Z0 decays based on a fourfold increase in statistics has been made using the 1990 and 1991 L3 data. The analysis of the dilepton events, muons and electrons, gives: chi(B) = 0. 121 +/- 0.017 (stat) +/- 0.006 (sys). Using the value of chi(d) measured at the UPSILON(4S) we derive the following limit for chi(s): chi(S) > 0.16 (90% CL).