With almost all votes counted after Sunday's elections, the former Communists were predicted to win 43.7 per cent and take 124 seats in the 240-seat parliament. The anti-Communist Union of Democratic Forces (UDF), the main challenger to the Socialists, trailed badly and was expected to finish with 23.9 per cent and 68 seats.
The remaining 48 seats will be distributed among the People's Union, which is a coalition of former UDF politicians and agrarians, the Movement for Rights and Freedoms, which represents Bulgaria's ethnic Turks, and the Bulgarian Business Bloc, dominated by a former emigre and fencing champion, Georges Ganchev.
The result makes Bulgaria the fourth country after Lithuania, Poland and Hungary to have returned former Communists to government since November 1992. Elsewhere, former Communists remain influential in countries such as Albania, Romania and Serbia.
The main exceptions to the trend are the Czech Republic, Latvia and Estonia, where non-Communist governments have made considerable progress in reforming the economy. In Slovakia, elections last September produced a victory for Vladimir Meciar, a populist nationalist, who was confirmed as prime minister last week.
As in other former Communist countries, one reason for the Bulgarian result was that many voters associated the economic hardships of the post-Communist era with the transition to democracy.
Bulgaria is suffering from an annual inflation rate of 120 per cent, and more than one in six workers is jobless. Another factor is the perception of many voters that anti-Communist democrats have been disunited and ineffective.
Like their colleagues in Poland, Bulgaria's former Communists have taken care to clean up their image, installing younger leaders and presenting themselves as supporters of reform "at an acceptable social cost". The Socialists' leader is Zhan Videnov, 35, an economist who studied in Moscow and says he favours Bulgaria's entry into the European Union.
The record of the reformed Communists is mixed. In Poland and Hungary, they wasted little time in dismissing officials and media personnel linked with their opponents, provoking accusations that they were conducting political purges.There has been greater continuity in foreign policy, with the goal of EU and Nato membership serving as common ground between the former Communists and the governments they replaced.
In economic policy, the former Communists of Poland and Hungary have stressed budgetary discipline and the battle against inflation in much the same way as the centre-right government of the Czech Republic. Poland's former Communists have sought to enhance their credibility by showing they can meet strict conditions set by the International Monetary Fund.
However, Bulgaria's Socialists have a more conservative reputation, and the pace of reforms is likely to be limited by the dire condition of the economy.