Dr. Arnold Jerome Friedhoff, a psychiatric researcher at New York University who investigated the biological underpinnings of mental disorders, died Wednesday at a rehabilitation center in Manhattan. He was 77 and a resident of the Upper East Side.

The cause was complications from a stroke he suffered several months ago, his family said.

He was known for his studies of brain chemistry and the effects of psychiatric drugs in illnesses like schizophrenia. His observations of biochemical changes in the metabolism of the neurotransmitter dopamine in schizophrenics helped usher in the development of new anti psychotic drugs.

A native of Johnstown, Pa., he received his undergraduate and medical degrees at the University of Pennsylvania in 1944 and 1947, and he completed his residency in psychiatry at Bellevue Hospital in 1954.

In 1955, he started his career at the N.Y.U., where he rose to full professor by 1966. When N.Y.U. started its Millhauser Laboratories in 1969, he was placed in charge and was director until last year.