Clavulanic acid (CA) was produced by Streptomyces clavuligerus in medium containing glycerol and soy meal or soy meal extract. With regard to growth and CA productivity, the microorganism showed significant differences if solid soy meal as such or its extract were applied as the major nitrogen source. If the extract is used, growth and CA production take place simultaneously and in the stationary phase the CA concentration is stagnant or reduces. If soy meal is used, growth is threefold faster and CA is only generated in the stationary phase. In the case of using the soy meal extract, the decrease of the CA concentration is mainly due to decomposition or re-metabolisation of CA in the presence of the microorganism. This conclusion is supported by in vivo and in vitro data on CA decomposition.