Re: question from John N. Wright. It's not clear what you are trying to quench but I assume it may be aldehyde reactivity with the antibodies. I never have to do that with formaldehyde based fixation but with glutaraldehyde based fixation I have been using 2mg/ml glycine as one component in my blocking solution (which also includes BSA, normal serum and usually a detergent all in PO4 buffer) Larry Ackerman [log in to unmask] The Laboratories of Lily & Yuh Nung Jan Voice (415) 476-8751 Howard Hughes Medical Institute UCSF, Box 0724, Rm U426 FAX (415) 476-5774 533 Parnassus Ave. San Francisco, CA 94143