Preservation of cisco (Coregonus artedii) and yellow perch (Perca flavescens) for 72 hr in 10% formalin or by freezing reduced median total length by 0.7–2.1% for both species and increased median condition factor by 6.3–9.4% for cisco and 4.8–8.8% for yellow perch. Formalin increased median weight by 1.8% for cisco and 5.0% for yellow perch; freezing and thawing reduced weight by 1.7–2.0% for each species. Changes in length, weight, and condition factor were not significant for unpreserved fish remeasured after 72 hr, suggesting that the above changes were not entirely due to errors in measurement. The study revealed that even small changes in length or weight due to preservation can produce large errors in condition factor.