  Leading three-baryon forces are derived within SU(3) chiral effective field
theory. Three classes of irreducible diagrams contribute: three-baryon contact
terms, one-meson exchange and two-meson exchange diagrams. We provide the
minimal non-relativistic terms of the chiral Lagrangian, that contribute to
these diagrams. SU(3) relations are given for the strangeness S=0 and -1
sectors. In the strangeness-zero sector we recover the well-known three-nucleon
forces from chiral effective field theory. Explicit expressions for the
lambda-nucleon-nucleon chiral potential in isospin space are presented.
