Microbes within palagonite-altered glass margins of pillow basalts have been identified at DSDP Hole 418A to a depth of 540 m below the top of the volcanic basement. Petrographic observations indicate that irregular palagonite alteration fronts radiating from fractures within the glass, are pervasive in layer 2 oceanic crust. Stable isotopic data (wholerock delta (super 13) C (sub PDB) values as low as -12.752) indicate that fractionation of carbon was partially controlled by organic processes. Electron microprobe backscatter images verify the presence of 1 um diameter microcaves along the irregular palagonite alteration fronts. X-ray mapping of the elements C, N, P, S, Ca, Mg, Fe, and K in these regions also implies extensive microbial alteration deep within the oceanic crust at DSDP Hole 418A.