A general methodology has been worked out for measuring the critical aggregate concentration (CAgC) of nonprobe molecules, i.e., molecules which are not kinetic or spectral probes. The coaggregation of target molecules (A’s); i.e., p-nitrophenyl dodecanoate (C12) and hexadecanoate (C16), have been studied in dioxane (DX)-H2O mixtures at 35-degrees-C by using n-decyl pyrenyl ketone (Py-11) and n-heptyl pyrenyl ketone (Py-8) as the fluorescent probes (B’s). The critical coaggregate concentrations of A with B (CoCAgC(A + B)’s) have been measured. The CAgC’s of target molecules (C12 and C16) are then obtained by extrapolation of the plot of CoCAgC(A + B) against probe concentration ([B]). All the CAgC values obtained are in good agreement with those measured kinetically.