Chemical fluctuations in high-energy nuclear collisions

Fluctuations of the chemical composition of the hadronic system produced in nuclear collisions are discussed using the $\Phi-$measure which has been earlier applied to study the transverse momentum fluctuations. The measure is expressed through the moments of the multiplicity distribution and then the properties of $\Phi$ are discussed within a few models of multiparticle production. A special attention is paid to the fluctuations in the equilibrium ideal quantum gas. The system of kaons and pions, which is particularly interesting from the experimental point of view, is discussed in detail.