Nonsense words of the form C′VC′VC′VC were recorded for the four voiceless fricatives of English [f,th,s,sh] in ten vowel environments by each of five male and five female talkers. The database was digitized at 16 000 samples/s and digital spectrograms were produced. Formant frequency values, F2 and F3, were measured by hand from the spectrograms at voicing onset and vowel midpoint for each CV transition. These data were examined in order to seek regularities of several possible forms: (1) invariant onset frequencies independent of speaker and vowel environment, (2) existence of locus frequencies that differ as a function of place of fricative articulation, but are similar across speakers, and (3) similar transition behavior (e.g., rising or falling F2 and/or F3) across speakers for a given vowel with no attempt to seek regularities across vowels. In all cases, distributions of transition-related measures across speakers for each place of articulation show disturbing amounts of overlap, even when male and female data are plotted separately. While it has often been said that [f] and [th] are distinguished perceptually by F2 and F3 transition behavior (because frication spectra are often quite similar), the data suggest that it will be difficult for a speech recognition device to make this distinction reliably from observed formant transition behavior in the general population. Some reassessment of the appropriate perceptual cues seems to be required. [Work supported in part by an NIH grant.]