Two four-dimensional TROSY triple resonance based experiments are presented for backbone assignment of high molecular weight proteins and protein complexes. The experiments, 4D-HNCACO and 4D-HNCOCA, establish correlations Of the form (C-13((i,i-1)alpha),C-13'((i,i-1)),N-15((i)),HN(i)) and (C-13((i-1)alpha),C-13'((i-1)),N-15((i)),HN(i)), respectively. Both sequences use an implementation of TROSY that offers improved sensitivity relative to previous sequences, critical for application to systems with correlation times on the order of 40-50 ns. The utility of the experiments is demonstrated by an application to a 46 ns tumbling complex of the 370 residue maltose binding protein and beta-cyclodextrin. Approximately 95% of the expected intra- and interresidue correlations are observed in the HNCACO and HNCOCA, respectively, with average signal-to-noise values of approximately 35/1. The methodology promises to be particularly powerful for applications to high molecular weight complexes comprised of a labeled fragment and unlabeled components or proteins with segmental labeling.