  We present electron-tunneling spectroscopy of oxygen over- and under-doped
Bi-2212 single crystals in a temperature range between 14 K and 290 K using a
break-junction technique. In over- and under-doped samples we observe a
pseudogap with T* = 280 - 290 K and T* > 290 K, respectively. In order to
explain the data we consider possible models for the pseudogap, namely, (i) a
precursor pairing; (ii) a charge-density-wave gap; (iii) a spin-gap due to
antiferromagnetic (AF) correlations. Analyzing all data we show unambiguously
that the only model which fits the data is a gap due to AF correlations.
