Hi Dr. Cartun, It has been many years since I worked in EM but I my recollection is that tissues could remain in 2% Glut indefinitely without detriment (for EM purposes). However, Osmium tetroxide had to have a limited exposure. Greg -- *Greg Dobbin* 1205 Pleasant Grove Rd RR#2 York, PE C0A 1P0 *Everything in moderation...even moderation itself**!*