A study investigated the usefulness of non-native speakers' subjective, relative word frequency estimates as a measure of second language proficiency. In the experiment, two subjective frequency estimate (SFE) tasks, one on French and one on English, were presented to French learners of English (n=126) and American learners of French (n=87). Subjects were university students studying in France. Each group received lists of 30 words (nouns and adjectives only), drawn from published frequency lists and presented alphabetically. Instructions to rank-order the words for frequency were given to each group in its native language. Results suggest the English list was easier to rank-order. In addition, while the performance of native speakers was better than that of non-native speakers on the English list, non-natives performed slightly but not significantly better on the French list. The inconclusive results suggest that SFEs can not provide indirect second-language (L2) proficiency measures. The close relationship of the two languages is seen as a possible confounding variable. The better performance of the American students is ascribed to the selectivity of the students' home institution. (MSE)