  We report on the measurement of four-body recombination rate coefficients in
an atomic gas. Our results obtained with an ultracold sample of cesium atoms at
negative scattering lengths show a resonant enhancement of losses and provide
strong evidence for the existence of a pair of four-body states, which is
strictly connected to Efimov trimers via universal relations. Our findings
confirm recent theoretical predictions and demonstrate the enrichment of the
Efimov scenario when a fourth particle is added to the generic three-body
problem.
