The big auction houses in New York are gearing up for their spring sales of Latin-American art this week. The top lots -- works by Diego Rivera and Rufino Tamayo -- are valued at around $1.5 million.

Paintings by Rufino Tamayo

Sotheby's will kick off proceedings with its top lot, 'El Fisgon' or 'The Voyeur', a 1988 painting by Rufino Tamayo, with an estimated value of $1.5 million.

Other painters in the modern sale include Astro Errante, Claudio Bravo, and Fernando Botero.

Of particular interest for Stein is a 1931 portrait by Cuban artist Wilfredo Lam of his wife, who died along with their infant son from tuberculosis shortly after their marriage.

"We're actually very excited by the Lam portrait of Eve. It's called "Eva". She's a discovery. Any time there's a discovery it's really something very interesting because you're actually bringing something not only to the market but to the knowledge on the artist. It's a very special painting," said Axel Stein, head of Latin Art Department, Sotheby's in New York.

Over at Christie's, whose auction is divided into two evenings on Wednesday and Thursday, a rare Diego Rivera is up for sale.

"Christie's Latin-American-Art auction of the 25th to 26th of May comprises in excess of 250 lots that range from 18th-century to the present. The sale is strong in respect to Latin-American modernism; in particular there is a strong concentration of the Mexican school of painting. One of the principal lots, more significant than the Tamayo or other artists, is a painting by Diego Rivera. It's a painting from a key period in the artist's life," said Virgilio Garza, head of Latin Art Department, Christie's New York.

Entitled "Nina con Rebozo", the Rivera comes from the private collection of Spanish opera legend Placido Domingo and is expected to fetch $1.5 million. Among the other 200-plus works in the Christie's sale are a Tamayo, a Lam, several Boteros, and a work by Miguel Covarrubias.