Quantitative analysis of radiolarian assemblages at Ocean Drilling Program Leg 199 Site 1219 provides new information on ocean temperature variations during a significant productivity event. This event (which occurs within radiolarian Zone RP-15) is marked by the accumulation of diatoms in association with highly diverse radiolarian faunas. The data collected for this present work include (1) counts of radiolarian diversity and (2) estimates of the abundance ratio of the radiolarian groups Spumellaria and Nassellaria. The radiolarian assemblages within the diatom-rich unit do not differ greatly from one another in their composition. There are, however, some long-term trends in faunal abundances, as indicated by changes in the nassellarian:spumellarian ratio. Particular changes in this ratio that possibly are related to the diatom event involve (1) the increase of the abundance of actinommids above the diatom-rich sediments and (2) the occurrence of abundance maxima of "robust" artostrobids at the beginning and during the terminal phase of diatom production. These changes can tentatively be interpreted as a reaction of specific radiolarian groups to the increase of diatom productivity in shallow waters. Taken together with the earlier onset of calcareous nannoplankton deposition, the diatom-rich unit can be interpreted as marking a short-term gradual change in sea-surface temperature, together with a change in the equatorial current system that involved the introduction of cold waters by lateral transport rather than the vertical upwelling of water masses derived from the southeastern regions of the Pacific Ocean.