We have plastically deformed hornblende in laboratory compression experiments. (101) twinning is a prominent deformation mechanism in single-crystal tests. The twin system is K1= (101), N1= (101), K2 = (100), N2 = . Translation gliding has also been induced on the system T = (100), t = . Although intragranular plastic deformation effects are not commonly observed in naturally deformed hornblende, we describe features in amphibolite from the southwestern Alps that are similar to those produced experimentally.