This study analyzed the pronunciation of English interdental fricatives by two native speakers of Turkish, focusing on whether there was systematic variation of forms according to the kind of discourse and the surrounding phonemes. Subjects were two adult Turkish learners of English as a Second Language, both of whom had been in the United States for 6 years. One was an advanced learner, the other an intermediate-level learner. Data were gathered in recordings of spontaneous speech, passage reading, and word list reading. Analysis of the transcriptions showed both speakers to be stable and consistent in the pronunciation, whether correct or incorrect, in all three situations. Neither had great difficulty pronouncing the voiced interdental. In pronouncing minimal pairs in the word list, both showed considerable symmetry in correct and incorrect pronunciations. Both had difficulty pronouncing the voiceless interdental fricative in certain consonant clusters and after back vowels in the same syllable. The intermediate-level English learner transferred pronunciation from some Turkish words. Implications for language teaching are discussed briefly. (Contains 10 references.) (MSE)