['Autologous hematopoietic stem cell transplantation (HSCT) has recently become a novel therapy for patients with new-onset type 1 diabetes (T1D). However, the optimal time points for HSCT are still unknown.', 'By using multiple low-dose streptozotocin (STZ)-induced T1D mice models, we performed syngeneic bone marrow transplantation (syn-BMT) in diabetic mice at various time points new-onset day 3 (n = 12); new-onset day 10 (n = 13); later-onset day 20 (n = 12); and day 40 (n = 7), respectively. At 120 days after syn-BMT, we examined pancreata histology, serum insulin, and CD4(+)CD25(+)FoxP3(+) T regulatory lymphocytes (Tregs).', 'Our previous results showed that syn-BMT can overcome diabetes when performed on day 10, but not at day 40. Our new data showed BMT only attenuated diabetes when done on day 3 or day 20. Moreover, the percentage of Tregs in the spleen correlated with the attenuation of hyperglycemia.'] Is time point important for effects of syngeneic bone marrow transplantation for type 1 diabetes in mice?