A cobalt-based Fischer-Tropsch catalyst, after 125 days of continuous synthesis, was found to have retained excessive amounts of synthesis products and was not pyroforic in air. Upon resuming synthesis, unusual reactions were observed for about 20 h. Carbon monoxide conversion was quantitative. The major product was methane, with a fairly flat distribution of paraffins and isoparaffins. Excessive end gas volumes and the presence of isoparaffins suggest that hydrocracking of the waxes deposited in the catalyst pores may have been the major reaction. Later, "normal" synthesis occurred. Catalyst activity measurements indicated a successful regeneration by the events.