The Experimental Mohole drilled during March and Apr. 1961 off Guadalupe Island, Mexico, penetrated about 2.5 m of red clay followed by 172.5 m of hemipelagic ooze, both calcareous and siliceous. The sediments range back to middle Miocene age. Below the ooze the drill encountered basalt. Three core sections, 1.5 m long, and six 5-25 cm subsections were available from the drilling for study. Analyses were made of grain size, water content, chlorinity and Ca and Mg in interstitial water, calcium carbonate, pH, Eh, total N, organic C, porphyrin pigments, hydrocarbons, amino acids (total and individual), and sugars. Attempts were made to culture bacteria from the sediments using a variety of media under aerobic and anaerobic conditions. Except for a few coarse grains in the red clay, all of the sediment is fine grained and deposited grain by grain; there is no indication of turbidites. The ratio of cations to chlorinity of interstitial water is nearly constant with depth except for an increase of Ca/Cl, possibly related to an irregularly lower pH at depth. Eh is positive throughout, showing oxidizing conditions. The sediments contain small concentrations of hydrocarbons, porphyrins, amino acids and sugars. Bacteria were cultured from only a few samples, and probably were introduced either during the drilling operation or subsequent sampling and culturing procedures. The data are discussed with respect to the salinity of the ocean during the period of sedimentation, and the origin and diagenesis of the sediment.