"This government is not for the corrupt nor for cowards," Mr Castro, one of the world's last surviving Communist leaders, declared at a formal state banquet on Monday evening as the ninth Ibero-American summit got under way.
King Juan Carlos of Spain raised his glass in return and saluted "authentic democracy, liberty, and scrupulous respect for human rights".
Even though there was a crackdown on street demonstrations ahead of the summit - including the arrest of 15 "counter-revolutionaries" - the Spanish Prime Minister, Jose Maria Aznar, openly met opposition spokesmen, as did the heads of state of Portugal and Uruguay. This was one condition set before a visit by King Juan Carlos and Queen Sofia, the first time in more than 50 years that Spain's reigning monarchs have visited the former colony.
After Miami, Madrid is the most important refuge for political exiles from Cuba. Spain's active participation in the conference sparked a boycott by Chile and Argentina, which oppose the campaign by the Spanish judge, Baltasar Garzon, to extradite the former Chilean military dictator General Augusto Pinochet from Britain to Spain.
One of the controversial points included in the summit's final declaration is a condemnation of "the unilateral and extra-territorial application of laws which infringe on international rights and intend to impose their own laws and ordinances on third countries".
The highlight of this gathering is expected to be tomorrow's face-off between a baseball team captained by the Venezuelan President, Hugo Chavez, a former professional player, and a crack Cuban squad led by 73-year-old Mr Castro. Mr Chavez is already warming up and perfecting his "wicked curve ball" in front of spectators.
With world attention focused on Havana, the United States presidential candidate Donald Trump campaigned in Miami before audiences of Cuban exiles who cheered when he decried recent calls to ease the American blockade of the Communist island.
Meanwhile, in Puerto Rico, a trial of six Cuban exiles who allegedly plotted to assassinate President Castro two years ago started in a San Jose courtroom. Among the accused is the head of the Miami-based Cuban American National Foundation, Jose Antonio Llamas. A US Coast Guard cutter stopped Llamas's yacht, La Esperanza, for a routine check off Puerto Rico in October 1997, when Mr Castro was attending a meeting on a nearby Venezuelan island.
On Monday, Coast Guard Lieutenant-Commander Brendan McPherson testified that the six businessmen, who all fled Cuba's revolution, told him they were on a fishing holiday. His officers then discovered two .50-calibre sniper rifles, ammunition, night-vision goggles, radios and satellite navigation equipment.
Mr Castro has accused the Cuban American National Foundation of trying to kill him - a charge the organisation denies. In his opening arguments at the trial, Ricardo Pesquera, a lawyer for the defence, said: "The only evidence of any murderer that you will hear about in this trial is Fidel Castro himself.''