To provide a screening method for an apoptosis-suppressing substance or an apoptosis-promoting substance, the application of which substances to pharmaceuticals or diagnostic drugs are expected, also to provide an apoptosis-suppressing substance or an apoptosis-promoting substance, since Bcl-2 family having apoptosis-suppressing or -promoting activities is deeply involved in many diseases.To attain the above object, VDAC-liposomes, an indicator substance such as fluorescent-labeled cytochrome c or isotope-labeled sucrose etc. capable of passing through VDAC (voltage-dependent anion channel), and a subject substance are incubated, and then concentration changes in the indicator substance, inside and outside the VDAC-liposomes before and after the incubation, are detected in order to estimate presence or absence of the apoptosis-suppressing activity or -promoting activity of the subject substance.