The binding of pyrene to a series of polysoaps of increasing hydrophobicity, the alternating copolymers of maleic acid and alkyl vinyl ether (alkyl = butyl, hexyl, decyl, dodecyl, and hexadecyl), has been investigated by spectrofluorometry and fluorescence decay time measurements, at constant pyrene concentration (almost-equal-to 5 X 10(-7) M) as a function of the polysoap concentration and degree of neutralization. The plots of the ratio I1/I3 of the intensities of the first and the third vibronic peaks in the pyrene fluorescence emission spectrum against the polysoap concentration were found to have the sigmoidal shape expected for the binding of pyrene to the hydrophobic microdomains present in the polysoap solutions. The same was true for the results of fluorescence lifetime measurements. The quantitative analysis of the I1/I3 data required use of a polysoap concentration-dependent binding constant and allowed us to estimate the fraction of alkyl side chains not involved in the formation of microdomains. The concept of cmc in polysoap solutions was discussed in light of these results. Finally, the fluorescence lifetime data were used to infer information on the dynamics of polysoaps in solution.