A study investigated the effect of properties of words and texts on the incidental learning of word meanings during normal reading. Subjects--352 students in third, fifth, and seventh grades--read either expository or narrative passages selected from grade-level textbooks, and after six days were tested on their knowledge of difficult words from the passages. Word properties investigated included length, morphological complexity, part of speech, conceptual difficulty, and the strength of contextual support for each word. Text properties included readability as measured by standard formulas, and several measures of density of difficult words. Results showed that, among the word properties, only conceptual difficulty was significantly related to learning from context. Among the text properties, learning from context was most strongly influenced by the proportion of unfamiliar words that were conceptually difficult, and by the average length of difficult words. (Author/HOD)