1. Schmidt, Helmut (1969). "Clairvoyance Tests with a Machine" Journal of Parapsychology vol.33

2. Schmidt, Helmut (1970). "PK Experiments with Animals as Subjects" Journal of Parapsychology vol.34

3. Schmidt, Helmut (1973). "PK Tests with a High Speed Random Number Generator" Journal of Parapsychology vol.37