We report transverse-field muon spin rotation studies of the magnetic field distribution n(B) in the vortex state of the high temperature superconductorBi2Sr2Ca1Cu2O8+&dgr;(Bi-2212) and present data on three sets of overdoped, nearly optimized and underdoped single crystals which to our best knowledge provide the first evidence that a two-stage melting transition of the vortex matter occurs under equilibrium conditions. In addition, we compare the TF-&mgr;SR results with those from DC-magnetization measurements and magneto-optic experiments on the same crystals. ©1999 American Institute of Physics.