From the Wikipedia entry on AJFA:
"And, in one of the more famous of Hetfield and Ulrich's controversies with bassist Jason Newsted, the album almost completely lacks bass guitar. The standard explanation for this combines Newsted's absence from the mixing sessions (where he might have asserted his opinion) and the lingering issue of his "newness" within the band following the tragic death of Cliff Burton in September 1986."
Sad but true? :-)