Stratigraphic distribution of the maximum diameter of the largest deep-water (> 1500 m water depths) calcareous trochospiral benthic foraminiferal tests in samples representing the past 120 m.y. shows that average values of the maximum diameter have doubled since Early Cretaceous time. Fluctuations in test size show six minima and six maxima. It is significant that the fluctuations correspond to changes in global climate and in deep-water dissolved oxygen conditions. This latter synchronism indicates that deep-sea foraminiferal test size was likely controlled by fluctuations in the level of dissolved oxygen or related factors in the deep ocean caused by global climatic changes.