It has been argued previously that the effect of NaCl on the aggregation number of sodium dodecyl sulfate (SDS) micelles is inconsistent with the observation that SDS micelles are fairly monodisperse. This inconsistency is resolved by arguing that the "effective micellar degree of dissociation", alpha, decreases with increasing aggregation number to an extent that cannot be detected from the effect of electrolyte on the critical micelle concentration.