We report on recent studies on two of our leading fluid candidates for high index immersion lithography, designated IF132 and IF169. The most recent fluid radiation durability results are discussed, leading us to define two important parameters, the fluid lifetime factor and the clean window dose related to suppression of window contamination through use of active recycle technology. Results of fluid-resist interactions, with water and high index fluids on four commercial resists, will be shown. These experiments include PAG leaching and contact angle measurements, resist profile and thickness changes due to preand post-exposure fluid contact, residues and defects from the fluid and from resist contact, and 36 nm hp imaging on an immersion interference printer.