Michoacan is the home state of the PRD leader, Cuauhtemoc Cardenas, son of General Lazaro Cardenas, one of the great heroes of the Mexican Revolution of 1910-17. He took a dissident 'democratic tendency' out of the PRI in the late 1980s, and gave the ruling party, which has been in power for more than 60 years, a nasty shock in the 1988 presidential elections.
The PRD claims that Mr Cardenas really defeated the PRI candidate, Carlos Salinas de Gortari, but the latter was declared the winner. The PRD has lost some of its momentum since then, even in Michoacan. The PRD lacks organisation, and Mr Cardenas, despite his pedigree, lacks charisma and an identifiable programme.
But the PRD regards itself as the upholder of the true Mexican revolutionary tradition, and has said it will take to the streets if the PRI candidate in Michoacan, Eduardo Villasenor, a pig breeder, is elected. The PRD accuses President Salinas of betraying the Revolution by halting the agrarian reform that General Cardenas set in motion in the 1930s and dismantling the imposing state-controlled economic apparatus assembled over the decades since 1910.
In Chihuahua, a huge and prosperous border state whose economy is closely linked to the United States, the business-oriented PAN is also confident of coming out on top. Its candidate, Francisco Barrio Terrazas, was defeated in the last election by the present PRI governor, Fernando Baeza Melendez, in what PAN claims was a rigged election. The PRI contender this time is Jesus Macias, a popular former mayor of the border boom town, Ciudad Juarez. PAN has warned its supporters that the PRI intends to rig the results this time, too.
In both contests, the PRI says it will win easily and has already rejected the opposition fraud charges. The ruling party has been revamping its image and modernising its organisation under a new young president, Genaro Borrego Estrada, former governor of the state of Zacatecas, and has come up with some attractive young candidates, far removed from the corrupt regional bosses, or caciques, of the past.
But both the PRD and PAN know that fraud accusations can bring results in present-day Mexico. Last year President Salinas overturned the results of local polls in the states of San Luis Potosi and Guanajuato after the opposition claimed the PRI had won by fraudulent means. Some observers feel that the PRI, which wants to show how responsive it is to public opinion these days, will be the loser whatever the result.