  A fraction of late B-type stars, the so-called HgMn stars, exhibit enhanced
absorption lines of certain chemical elements, notably Hg and Mn, combined with
an underabundance of He. For about a decade now the elements with anomalously
high abundances in HgMn stars are known to be distributed inhomogeneously over
the stellar surface. Temporal evolution of these elemental spots have been
reported in a few HgMn stars, first secular evolution of the mercury spots in
alpha And, and recently also a fast evolution of yttrium and strontium spots in
HD 11753. The fast evolution of spots in HD 11753 is combined with a slower
change in the overall abundance of the affected elements. In this paper I
review what is known of elemental spots in HgMn stars and their secular and
fast temporal evolution.
