A reference database of the major soluble proteins of the primary root of the maize inbred line B73 was generated 5 days after germination (DAG) using a combination of 2-DE and MALDI-TOF MS. A total of 302 protein spots were detected with CBB in a pH 4-7 range and 81 proteins representing 74 distinct Genbank accessions were identified. Only 28% of the major proteins identified in 5 DAG primary roots were identified in similarly analyzed 9 DAG primary roots documenting remarkable changes in the accumulation of abundant soluble proteins early in primary root development.