The respiration electrode - a new type of microbial sensor comprising small amounts of viable microorganisms on an oxygen electrode - was used for characterization of the physiological state of cells by measuring the change of respiration after substrate addition, (for example glucose by Bacillus subtilis as well as glucose and methanol by Candida boidinii). This respiration parameter - designated as acceleration of respiration - alters characteristically during a growth cycle, and is useful in following the physiological state of microorganisms.