A non-denaturating isoelectric focusing (ND-IEF) gel electrophoresis protocol has been developed to study and identify uranium (U)-protein complexes with laser ablation-inductively coupled plasma mass spectrometry (LA-ICP MS) and electrospray ionization mass spectrometry (ESI-MS). The ND-IEF-LA-ICP MS methodology set-up was initiated using in vitro U-protein complex standards (i.e., U-bovine serum albumin and U-transferrin) allowing the assessment of U recovery to 64.4 ± 0.4 %. This methodology enabled the quantification of U-protein complexes at 9.03 ± 0.23, 15.27 ± 0.36, and 177.31 ± 25.51 nmol U L-1 in digestive gland cytosols of the crayfish, Procambarus clarkii, exposed respectively to 0, 0.12, and 2.5 μmol of waterborne depleted U L-1 during 10 days. ND-IEF-LA-ICP MS limit of detection was 19.3 pmol U L-1. Elemental ICP MS signals obtained both in ND-IEF electropherograms and in size exclusion chromatograms of in vivo U-protein complexes revealed interactions between U- and Fe- and Cu-proteins. Moreover, three proteins (hemocyanin, pseudohemocyanin-2, and arginine kinase) out of 42 were identified as potential uranium targets in waterborne-exposed crayfish cytosols by microbore reversed phase chromatography coupled to molecular mass spectrometry (μRPC-ESI-MS/MS) after ND-IEF separation. [Figure not available: see fulltext.] © 2013 Springer-Verlag Berlin Heidelberg.