A device and a method for rapidly determining the effectiveness of sterilization or disinfection processes are provided. The method involves contacting a biological indicator containing a known number of live spores to a sterilization or disinfection process. When the spores are killed, the minerals in the spores are released. Water is contacted with the dead spores to form an aqueous solution. A parameter related to the concentration of a mineral in the aqueous solution is measured. The effectiveness of the germicidal process is determined from the parameter and the initial number of spores in the biological indicator. Measuring the parameter by measuring the conductivity of the aqueous solution is particularly effective and sensitive.