

Analyses of strong-interaction data consisting of level shifts, widths and yields in strange atoms of K− mesons and Σ− hyperons are reviewed. Recent results obtained by fitting to comprehensive sets of data across the periodic table in terms of density-dependent optical potentials are discussed. The introduction of density dependence generally improves significantly the fit to the data, leading to novel results on the in-medium hadron-nucleon t matrix t(ρ) over a wide range of densities up to central nuclear densities. A strongly attractive K−-nuclear potential of order 150–200 MeV in nuclear matter is suggested by fits to K−-atom data, with interesting possible repercussions on