As previously reported the equation logy 0 − logy=ta log (1+b t) has been found to describe the course of inactivation of poliovirus by formaldehyde. The present paper reports and discusses different methods of fitting this equation to experimental data. With the aid of the methods described data recently published byHaas et al. and byTimm et al. are analyzed. Those ofHaas et al. show an extraordinarily good fit and, thus, confirm our previous findings. On the other hand, the data ofTimm et al. do not fit the formula. Attention has been directed to certain inadequacies in the technic applied by these authors which seem to offer a plausible explanation for the discrepancies in results.