COULD THERE BE A 4TH GENERATION OF QUARKS WITHOUT MORE LEPTONS

We investigate the possibility of adding a fourth generation of quarks . We also extend the Standard Model gauge group by adding another SU(N ) component. In order to cancel the contributions of the fourth genera tion of quarks to the gauge anomalies we must add a generation of ferm ions coupling to the SU(N) group. This model has many features similar to the Standard Model and, for example, includes a natural generalisa tion of the Standard Model charge quantisation rule. We discuss the ph enomenology of this model and, in particular, show that the infrared q uasi-fixed point values of the Yukawa coupling constants put upper lim its on the new quark masses close to the present experimental lower bo unds.