During DSDP Leg 55, volcanic rocks were recovered at Sites 430, 432, and 433, on Ojin, Nintoku, and Suiko seamounts, respectively, in the Emperor Seamount chain. Of the five lava flows recovered at Hole 430A, the upper four flows are typical hawaiites and the lowest flow is tholeiite. Three lava flows of alkalic basalts recovered at Hole 432A on Nintoku Seamount are petrographically and chemically similar to the analogous rocks from the Hawaiian Islands. Ninety-six cooling units, from 163 to 550 meters sub-bottom, were sampled at the re-entry Hole 433C. Most of them are lava flows and others are secondary thin flows or flow lobes from fissures of basic flows. The three uppermost flows are alkalic basalts. Eight individual cooling units of picrite-basalts (Flow Units 4A-4H) occur below them. The underlying sequence of flows is composed almost entirely of tholeiites: only four flows are transitional toward alkalic basalts, and one of them is picrite-basalt. In spite of the nearly complete absence of sedimentary and pyroclastic interbeds between the flows, good recovery permitted us to distinguish boundaries of cooling units and determine their thicknesses. We calculated the thicknesses of tholeiitic and transitional basalt flows in the flow sequence of Hole 433C assuming that the flows fill all void space proportionally to the recovery in each flow. Most cooling units range in thickness from 0 to 2 meters (Figure IA). This is the interval defining not only primary lava flows, but also secondary flows or flow lobes. A minimum in the interval from 1.25 to 1.5 meters (Figure IB) apparently is a boundary between lava flows and flow lobes. As a whole, this agrees with data obtained in the Hawaiian Islands, where thickness of the tholeiitic flows is commonly not less than 1 meter (Macdonald and Abbott, 1970), although very thin flows can be found occasionally. This study is undertaken to determine petrologic and chemical heterogeneities caused by crystallization conditions and alteration.