The appropriateness of using locus equations in a study of voiceless consonants is examined. The consonants investigated are the stops /t k/ and the fricatives /theta s integral/. The slope value of the locus equation, indicating degree of coarticulation in the CV syllable, is compared with electropalatographic (EPG) data on coarticulation. It is shown that, overall, there is a very poor correlation between locus equation and EPG data as regards coarticulation. It is also shown that more accurate locus equation results - in terms of their correlation with EPG data - are obtained for stop consonants when F2 onset is sampled at stop release, rather than at the onset of voicing for the vowel. Finally, results for the voiceless consonants are compared with results for their homorganic voiced counterparts. Whilst there is no significant difference between voiced and voiceless consonants in the EPG data, there is a significant difference between voiced and voiceless consonants in the locus equation data. These results suggest that locus equations cannot provide invariant cues for stop and fricative place of articulation across the voiced-voiceless distinction.