Witnesses said Mrs Abiola was shot in the head and her driver wounded in the mouth. Surgeons at a Lagos hospital fought unsuccessfully to save her life. "She didn't make it", was the terse verdict of Dr Alex Eneli, at the capital's Eko Hospital. Mrs Abiola was shot through the forehead. Doctors say there was no exit wound.
Police are searching for a grey car that fled the scene of the attack near the Abiolas' home. The identity of the gunmen is unknown.
Mrs Abiola was a prominent figure in the campaign to secure the release from detention of her husband, Chief Moshood Abiola, widely regarded as the winner of the 1993 presidential election. The vote was annulled by the former ruler, General Ibrahim Babangida.
Chief Abiola has been held in prison on a treason charge since June 1994 for having proclaimed himself president in defiance of the military government of General Sani Abacha who seized power almost three years ago. The regime stands accused of corruption and of a blatant disregard for human rights.
Though not untainted by rumours of corruption, Chief Abiola is a symbol for many dissatisfied Nigerians, particularly in the Yoruba heartland of the south-west. A Muslim and a Yoruba, he bridges the divide between the alienated Christians of the south and the Muslims of the northern Hausa- Fulani dynasty, who dominate the power structures.
Nigeria has been isolatedand criticised by the international community since the executions in November 1995 of the writer Ken Saro-Wiwa and eight other minority activists.
Last autumn, General Abacha announced a three-year transition period for a return to civilian rule. But, as the last 13 years of almost constant military rule have shown, the introduction of multi-party democracy is not a foregone conclusion.
Africa's most populous nation has been ruled by military regimes for more than 25 out of its 35 years of independence. In that time, several dictators have made promises of a transfer to civilian rule, which they have not carried out.