Latent fingerprints are developed by exposing them to vapors generated from a thin film of a storage stable cyanoacrylate monomer and a thixotropic additive in sufficient amount to render the composition substantially non-flowable. The monomer film should have a surface area of at least 129 sq. cm.An envelope package for the monomer composition has inner polyethylene surfaces. The envelope may be peeled open to expose the inner surfaces coated with a film of the composition.