The American Political Science Association has appealed to the government of Saudi Arabia to release Matrouk al-Faleh, a political scientist and one of the country’s leading human-rights activists, who was arrested in Riyadh on May 19.

“The arrest and detention of Dr. Matrouk al-Faleh appears to be a case of his being held solely for the nonviolent exercise of his right to freedom of expression and association,” writes Dianne Marie Pinderhughes, president of the association.

The Saudi authorities have not disclosed why Mr. Faleh was arrested, but it was shortly after he publicly criticized the harsh and overcrowded conditions his clients Abdullah and ‘Issa al-Hamid face as prisoners. Amnesty International believes his arrest is in connection with that criticism.

Mr. Faleh was providing legal representation for the Hamid brothers, who are fellow human-rights activists found guilty of “incitement to protest” after supporting a demonstration outside the prison.

Two days before his arrest, in an e-mail message to human-rights activists and journalists, Mr. Faleh described the “laborious” visiting procedures and likened the visiting area to a chicken coop.

Mr. Faleh’s family has had no contact with him since the Saudi secret police arrested him at King Saud University, in Riyadh, where he teaches. There have been no reports of his condition. Amnesty International says he is at risk of torture and other ill treatment.

Ms. Pinderhughes, of the political-science association, has joined the calls on Saudi officials to provide assurance that Mr. Faleh is being held in “safe and humane conditions, with access to his family and to medical and legal assistance.” —Andrew Mills