This paper reports a corpus-based genre analysis of the structural and linguistic evolution of medical research articles (RAs) written in English. Towards that end, we analyzed the frequency of occurrence of the 11 moves identified by Nwogu (1997), of the three most frequently used verb tenses (simple past, simple present and present perfect) and of the first person pronouns in 25 RAs published between 1985 and 1989 (Corpus A), on the one hand, and 25 RAs published between 2000 and 2004 (Corpus B), on the other. The results obtained were compared by means of Chi-square test or Mann-Whitney U test with those reported in previous research. Our findings indicated that Moves 1 and 6 changed from "optional" to "obligatory" (c.f. Nwogu, 1997) whereas Move 9 switched from "obligatory" to "optional". Move 8 remained an "optional" move, though significant difference was found in its frequency of occurrence between the two corpora (p = 0.015). Regarding verb tenses, we found that the frequency of the simple past significantly increased in Move 3 (p = 0.001) as well as that of the simple present in Move 10 (p = 0.004). The frequency of the present perfect significantly decreased in both Move 3 (p = 0.001) and Move 10 (p = 0.001). Regarding the first person pronoun, we found significant inter-corpus differences in the total number of the plural form of the first person pronoun and its related cases (p = 0.001) and in their frequency of occurrence in the Methods, Results, and Discussion sections (respectively, p = 0.001). These findings are discussed in light of the evolution of medical science and attitude changes of medical RA writers. (Contains 5 tables.)