Even before AIDS was recognized as a syndrome, Berkowitz became concerned about protecting his clients, many of whom were married, from sexually transmitted diseases. He met physician Joseph Sonnabend and became a patient, learning from Sonnabend the practices for risk reduction that would later become known as safe sex.[1] His early work with Sonnabend and singer and activist Michael Callen noted behaviors including drug use, multiple sexual partners, and unsafe sexual practices in the gay community for transmission.