Single-walled nanotube (SWNT) synthesis is studied in a pyrolysis flame configuration seeded with ferrocene as a catalyst precursor reagent. The concentration of ferrocene is prominent among the factors that determine SWNT inception, growth, and catalyst particle deactivation. This reflects ferrocene's role as metal catalyst precursor and as a source of cyclopentadiene species upon its thermal decomposition. Results with different reactant gas mixtures and flows are presented and interpreted in light of a SWNT synthesis mechanism and catalyst deactivation processes.