The acquisition of two drawings, two sculptures and three oil paintings crowns two years of negotiations during which three big Spanish banks put up the cash for the purchase - pounds 15m - in lieu of paying tax. The pieces date from the Civil War years of the 1930s and complement Picasso's cry of grief and rage, Guernica, jewel of the Reina Sofia's collection.
Claude Picasso, the artist's grandson, said recently that the family was prepared to negotiate the sale of other works to the museum, despite having neither the need nor the inclination to part with any of the enormous quantity of material still in family hands.
Madrid has long felt sore about being last in the queue for important Picassos. The bulk of the artist's work, from his young and old period, is in the Picasso Museum in Paris or that of Barcelona. The Reina Sofia has tried to fill a gap by acquiring works from the artist's middle years, but recognises it will never be able to match the other collections.
Untypically for Spain, "Operation Picasso" - the Socialists' most ambitious cultural project - survived last year's change in government, and the former culture minister, Carmen Alborch, attended the unveiling last week to remind everyone that it had been her idea. Her conservative successor, Esperanza Aguirre, thanked her for the initiative.
The Guernica painting itself is at the heart of a tug-of-war between the Reina Sofia and the Guggenheim Museum in Bilbao, a futuristic building by the American architect Frank Gehry due to open this summer. The Guggenheim wants to borrow Picasso's homage to the bombed Basque village as part of its inaugural exhibition, but the Reina Sofia says the painting is too fragile to be moved. A spokeswoman said this week the museum had received no formal request from the Guggenheim.