Adrian Mathias has written some excellent articles comparing the specific set theory used by Mac Lane and used in other parts of category theory.

 - His article [The strength of Mac Lane set theory](http://www.dpmms.cam.ac.uk/~ardm/maclane.pdf) is a detailed analysis of the strength of Mac Lane's set theory in comparison with other theories. 

 - Adrian Mathias, "What is Mac Lane missing?" (a comment on the foundational stance of Saunders Mac Lane; [MR 94g:03010](http://www.ams.org/mathscinet/search/publdoc.html?arg3=&co4=AND&co5=AND&co6=AND&co7=AND&dr=all&pg4=AUCN&pg5=TI&pg6=PC&pg7=ALLF&pg8=ET&review_format=html&s4=&s5=&s6=&s7=94g%3A03010&s8=All&vfpref=html&yearRangeFirst=&yearRangeSecond=&yrop=eq&r=2&mx-pid=1233815); published with a reply by Mac Lane, [MR 94g:03011](http://www.ams.org/mathscinet/search/publdoc.html?arg3=&co4=AND&co5=AND&co6=AND&co7=AND&dr=all&pg4=AUCN&pg5=TI&pg6=PC&pg7=ALLF&pg8=ET&r=1&review_format=html&s4=&s5=&s6=&s7=94g%3A03011&s8=All&vfpref=html&yearRangeFirst=&yearRangeSecond=&yrop=eq), in Set Theory of the Continuum, ed. H. Judah, W.Just, H.Woodin; Mathematical Sciences Research Institute Publications Volume 26, Springer-Verlag, 1992.)

 - See also Adrian Mathias, "[Strong statements of analysis](http://www.dpmms.cam.ac.uk/~ardm/strong.pdf)." 

 - Further papers available on [Mathias's web page depository](http://www.dpmms.cam.ac.uk/~ardm/).