Temperature and the concentrations of several major species, twenty one hydrocarbon intermediates ranging in size from C2H2 to C12H10, and soot were measured in an axisymmetric, atmospheric-pressure, laminar, coflowing methane/air non-premixed flame. Gas samples were extracted from the flame with a quartz microprobe and analyzed on-line with single-photon photoionization mass spectrometry. Horizontal profiles were obtained with millimeter spatial resolution at six heights above the burner surface that spanned the soot-containing portion of the flame. The flame contained numerous acetylenic species, benzene, many substituted benzenes, and several two or three-ring compounds at concentrations exceeding one part per-million. The most abundant intermediate hydrocarbons were acetylene, then allene and/or propyne and benzene. The maximum concentrations of most linear hydrocarbons stayed roughly constant at different heights, whereas polyacetylenes and aromatics accumulated with increasing height, with larger or more substituted aromatics peaking higher in the flame. At the lowest height where methane was undetectable, soot and all other hydrocarbons were also undetectable.