FLUX-LINE-LATTICE MELTING IN BI2SR2CA2CU3O10

We have performed de magnetization studies in the c-axis-oriented bulk Bi2Sr2Ca2CU3O10 compound. The penetration depth lambda(ab)(T) is extr acted from reversible magnetization data M(H) taking into account fluc tuations of the vortices. An ''irreversibility line'' is quantitativel y compared with predictions of flux-line-lattice (FLL) melting models. The results strongly suggest that the ''irreversibility line'' near T -c is associated with melting of FLL caused by thermal fluctuations.