Protein abundance differs from a few to millions of copies per cell. presents an excellent model for studies on codon bias and differential gene expression because transcription is broadly unregulated and uniform across the genome. is also a major human and animal protozoal pathogen. Here， an experimental assessment， using synthetic reporter genes， revealed that GC3 codons have a major positive impact on both mRNA and protein abundance. Our estimates of relative expression， based on coding sequences alone (codon usage and sequence length)， are within 2-fold of the observed values for the majority of measured cellular mRNAs (n > 7000) and proteins (n > 2000). Our estimates also correspond with expression measures from published transcriptome and proteome datasets from other trypanosomatids. We conclude that codon usage is a key factor affecting global relative mRNA and protein expression in trypanosomatids and that relative abundance can be effectively estimated using only protein coding sequences.