OBJECTIVE: To study the survival motor neuron (SMN) gene exon 7 and 8 and neuronal apoptosis inhibitory protein (NAIP) gene exon 5 and 6 in Chinese patients with Type Ⅰ～Ⅲ SMA, and to confirm the relationship between the deletions of SMN and NAIP genes with SMA phenotype. METHODS: PCR and PCR-enzyme methods were used to detect the deletions of NAIP gene exon 5 and 6 and SMN gene exon 7 and 8 in 15 SMA (Ⅰ～Ⅲ) patients, 20 healthy relatives and 30 normal controls. RESULTS: Deletions of exon 7 and 8 of the telomeric SMN gene were 4/4, 2/3, 1/8 in Type Ⅰ, Ⅱ, Ⅲ SMA patients, respectively. One patient with Type Ⅱ lacked exon 7 but retained exon 8. No deletion was found in the controls (0/50). No deletion of exon 5 and 6 of the NAIP gene was detected in the patients, healthy relatives and controls. CONCLUSIONS: Deletions of SMN gene exon 7 and 8 examined by PCR-enzyme digestion could be recommended as an accurate gene diagnostic method for SMA with Type Ⅰ and Ⅱ. However, the method was not as useful in Type Ⅲ as in Ⅰ and Ⅱ for the diagnosis of SMA. The frequency of NAIP deletion was lower in Chinese SMA patients.