The determination of limit of quantification (LOQ) is one of the tasks specified in the validation process of a microbiological method. So far a detailed procedure for doing it is still lacking. Given the LOD (limit of detection), or data for estimating the LOD, we propose a procedure for determining the LOQ based on a Poisson confidence interval and a probability interval. This approach assures that data generated with mean at the LOQ will be higher than the LOD with high probability. We determine the required number of replicates in the validation test used to determine the LOD and the LOQ using the negative binomial probability density function that models over-dispersion of growth media plate count data in validation tests. The objective is to facilitate the determinations of some parameters commonly used in microbiological testing, such as setting control limits and suitable number of growth media plate counts. Key words: microbiological methods, limit of detection (LOD), limit of quantification (LOQ), confidence intervals.