Abstract Objectives: Successful further treatment of Wilms tumors (WTs) after preoperative chemotherapy and surgery depends on correct histopathologic risk stratification, including quantification of remaining blastemal elements. In the present study, we assessed the usefulness of protein markers for the detection of WT blastema. Methods: Expression of the candidate blastemal protein markers CITED1, SIX1, and CD56 was evaluated by immunofluorescence regarding sensitivity and specificity for staining blastema in a tissue microarray containing cores from 30 WTs, a small number of rarer pediatric renal neoplasms, and normal postnatal kidney. Results: CITED1, SIX1, and CD56 were expressed in blastema in 100%, 89%, and 74%, respectively, of the WTs with this component present. However, they were also expressed in 64%, 25%, and 79%, respectively, of epithelial WT elements and 48%, 52%, and 62%, respectively, of stromal WT elements. Conclusions: SIX1 showed the highest specificity, CITED1 the highest sensitivity, and CD56 low specificity and sensitivity for detection of postchemotherapy WT blastema. Cytokeratin staining proved to be a useful way to determine rudimentary tubular elements not readily recognized by routine staining.