The kinetics of resealing, defined as the recovery of impermeability to macromolecules, of well-washed human erythrocyte ghosts has been determined. The resealing process is first-order at temperatures above 20-25 degrees C in isotonic salt, with rate constants ranging from 0.01-0.15 min-1. Below 20 degrees C, resealing occurs, but a long lag period is observed. Other erythrocyte membrane properties suggest a transition at about 20 degrees C, and it is possible that resealing rates are a measure of membrane fluidity. A temperature-induced reduction of resealed ghost volume was also observed. The effect of ionic strength on resealing parameters was determined. Low ionic strength buffers prevent resealing, which is also consistent with resealing as a lipid-related event. The effect of microtubule disrupting drugs and changes in the method of preparing ghosts are also described.