  This paper reviews some of the recent observational results on stellar mass
black hole candidates. Over the last decade, much of the progress in this field
has been achieved through the study of transient X--ray binary sources which
shine only sporadically in the X--ray sky and undergo much larger luminosity
variations then most persistent sources. There are currently six stellar--mass
black hole candidates for which the mass of the compact object is estimated to
be well above the maximum neutron star mass. The three most recently identified
black hole candidates of this kind belong to a class of transient X--ray
sources with peculiar spectral properties. Several new transients of this class
are being discovered and studied every year thanks to more continous monitoring
of the X--ray sky. Many of them are likely to contain other black hole
candidates. The growing number of candidates and the large luminosity
variations (and therefore, accretion rate variations) in transient sources will
allow to study the chacteristics of accreting black holes with an unprecedented
detail.
