In this study 874 mouse embryos were allocated to six groups including a control, co-culture, and four groups that underwent partial zona dissection (PZD): at the 2-cell (PZD-2) and morula stages (PZD-M) both with and without co-culture. Rates of complete blastocyst hatching on day 5 increased in the following order: control, co-culture alone, PZD-2 alone, PZD-M alone, PZD-2 with co-culture and PZD-M with co-culture (P < 0.00001). PZD-M led to significantly higher rates of complete blastocyst hatching compared to PZD-2 (P < 0.03). This study showed also that co-culture apparently compensates for any minor damage incurred during the PZD technique at the 2-cell and morula stages, (P < 0.01 and P < 0.01) respectively. Therefore PZD and co-culture seem mutually beneficial techniques that promote early blastocyst hatching in the mouse.