In a corresponding move, they transferred third baseman Kevin Youkilis to the 60-day DL to clear a 40-man spot for Ishikawa.
The Yankees have struggled to fill first base all season, with starter Mark Teixeira missing most of the season with various injuries. Ishikawa would provide them with a solid defensive option who probably won't give much with the bat.
Ishikawa was 2-for-17 for the Orioles this year, but they did not need him as they have Chris Davis currently manning the first base spot. He has also played for the Giants and Brewers, but has never been an exceptional player.
With Alex Rodriguez and Derek Jeter both getting closer to returning every day, the Yankees are not far away from getting their regulars back and not having a need for replacement-level guys such as Ishikawa.