Tyrosinase shows a lag period in its action on monophenols (l-tyrosine). We propose an approximate analytical solution for the lag period, which fulfils the dependences with regard to initial enzyme concentration, and initial monophenol concentration. Furthermore, from a study of the dependences of the lag period on these variables, we can determine experimentally the o-diphenol concentration in the steady state. The Michaelis constant of the o-diphenol in the presence of the monophenol can be determined from the relationship between the o-diphenol concentration in the steady state and the initial monophenol concentration, taking into consideration the experimentally calculated Michaelis constant for the monophenol substrate. Although this Michaelis constant is much lower than the Michaelis constant for diphenol in the absence of monophenol, the binding site is the same. A kinetic analysis of the action mechanism of tyrosinase explains this difference in the values of the Michaelis constants.