The planktonic foraminiferal biostratigraphy of cores 22–45 from DSDP Site 593 (Challenger Plateau, Tasman Sea) is related to New Zealand onshore Miocene stages (Altonian‐Tongaporutuan). An excellent succession of Altonian events at the site allows the stage to be divided into three informal zones. Upper Clifdenian and some lower Lillburnian horizons are highly condensed, or missing; this possible hiatus near 393.5 m is at a prominent litho‐stratigraphic boundary. A pronounced increase in representation of dextrally coiled Globorotalia miotumida immediately above the base of Tongaporutuan Stage in two onshore sequences is also recorded at Site 593. It may provide a useful criterion for the boundary in oceanic sequences lacking the Bolivinita quadrilatera group, as well as defining a basal Tongaporutuan zone. The highest occurrence of Globoquadrina dehiscens near the top of core 28 is well defined and possibly provides a useful intrastage event.