A cowpea flour-water mixture was fermented by its indigenous microflora at different temperatures (21.5-38.4 degreesC) and for different times (5.8-34.1 h). Response surface methodology was applied to find quadratic equations showing the relationship between the fermentation responses (i.e. the % acidity as lactic acid and the pH) and the fermentation variables (i.e. time and temperature). The time of fermentation was pronounced more significant than fermentation temperature suggesting that time should be controlled more carefully than the temperature. The activation energy (E-a) was found as 53.0 kJ/mol from an Arrhenius-type equation. (C) 2001 Elsevier Science Ltd. All rights reserved.