We analyzed 91 patients. Results of the RSB: 40 HD (44 %), 34 no Hirschsprung (37.4 %) and 17 NC (18.7 %). Sensitivity = 97.5 %, specificity = 97.1 %, not including the NC (1 false positive, 1 false negative). Results depending on the staining: ACE (n = 58) (%) ACE + C (n = 33) (%) p Sensitivity 96 100 1 Specificity 94.7 100 1 NC 24.1 9.1 0.077 Results depending on the age: <1.5 m (n = 27) (%) >1.5 m (n = 64) (%) p Sensitivity 92.3 100 0.325 Specificity 100 96.8 1 NC 40.7 9.4 0.001 CONCLUSION: Calretinin decreases the rate of inconclusive results, but not significantly. The percentage of inconclusive results decreases in patients olders than 1.5 m. Further studies are necessary to determine if this technique is useful to improve RSB results in infants younger than 1.5 months.